JP7468231B2 - Mail control device and program - Google Patents

Description

The present invention relates to an email control technology that encrypts and transmits attachments to emails sent from a terminal.

When important confidential information is included in an email, the erroneous sending of the email becomes a major problem. One method for dealing with such erroneous sending is to include a technique in which, when important confidential information is sent by email, the confidential information is written in an attachment, encrypted with a password, and attached to the outgoing email, and the password is notified to the recipient in a password notification email separate from the outgoing email. This makes it possible to avoid the risk of confidential information leaking, since the attachment cannot be decrypted unless the password notification email is sent to the incorrect recipient (see, for example, Patent Document 1).

In Patent Document 1, an email relay device is configured to encrypt an attachment attached to an email sent from a source terminal, send the encrypted file to a destination terminal, and, based on a notification instruction from the source terminal of the email, generate a password notification email containing an encryption password for decrypting the encrypted file, and send the password notification email to the destination terminal of the email.

In Patent Document 1, an encrypted file obtained by encrypting an attachment from a sending terminal is sent to a destination terminal, and the destination terminal is notified of the encryption password by a separate email, so that only a legitimate terminal can decrypt the encrypted file and obtain the original attachment.

JP 2008-187280 A

In Patent Document 1, the email relay device generates a password notification email based on a notification instruction from the email sender terminal and sends it to the email destination terminal, thereby reducing the workload of creating the password notification email on the email sender terminal. However, there is no disclosure of how the email sender terminal should respond if there is an error in the destination of the email.

The present invention is intended to solve these problems, and aims to provide an email control device that reduces the workload on the sending terminal and allows the sending terminal to take action if there is an error in the destination of an outgoing email.

In order to achieve such an object, the present invention provides a mail control device that, when a file is attached to an outgoing mail from a sender terminal, encrypts the attachment and transmits the attachment to a destination terminal, the mail control device comprising: an encryption processing unit that encrypts the attachment; a mail processing unit that transmits the outgoing mail with the encrypted attachment to the destination terminal; a storage unit that stores the outgoing mail with the encrypted attachment; and a password notification processing unit that creates a password notification mail including an encryption password for decrypting the encrypted attachment, the mail processing unit:
The password notification email is sent to the sending terminal, with the destination address of the sent email stored in the memory unit written in the destination address of the password notification email, the password notification email returned from the sending terminal is received, and the password notification email is sent to the destination address of the password notification email received from the sending terminal.

The email processing unit may also compare the destination address of the password notification email received from the source terminal with the destination address of the outgoing email stored in the storage unit, and create an email requesting the discarding of the outgoing email to be sent to a specific destination address that is the destination of the outgoing email but not the destination of the password notification email, the email containing one specific destination address or multiple specific destination addresses, and send the email to the destination terminal of the specific destination address.

The email processing unit may also send the discard request email to the source terminal, and after the source terminal confirms the sending of the discard request email, send it to a destination terminal with the specific destination address.

The email processing unit may also notify the sending terminal of the result of sending the discard request email.

The email processing unit may also send the discard request email to the destination terminal of the specific destination address and to the source terminal.

The mail control program according to the present invention is a mail control program executed in a mail control device that encrypts an attachment and sends it to a destination terminal when a file is attached to an outgoing mail from a sending terminal, and causes the mail control device to execute an encryption step of encrypting the attachment, a step of sending the outgoing mail with the encrypted attachment to the destination terminal, a storage step of saving the outgoing mail with the encrypted attachment, a step of creating a password notification mail including an encryption password for decrypting the encrypted attachment, a transmission step of sending the password notification mail to a destination address of the password notification mail received from the sending terminal, a step of sending the password notification mail to the sending terminal with the destination address of the outgoing mail saved in the storage step written in the destination address of the password notification mail, a step of receiving the password notification mail returned from the sending terminal, and a transmission step of sending the password notification mail to the destination address of the password notification mail received from the sending terminal.

According to the present invention, after sending an outgoing email with an encrypted file attached, a password notification email containing the destination address of the outgoing email is sent to the sending terminal to the destination address of the password notification email, and the password notification email is sent to the destination address of the password notification email received from the sending terminal. This reduces the workload on the sending terminal and provides an email control device that can handle cases where there is an error in the destination address of the outgoing email.

FIG. 2 is a block diagram showing the configuration of a mail control device. FIG. 2 is an explanatory diagram showing an example of the structure of an outgoing email. FIG. 11 is an explanatory diagram showing an example of the structure of an outgoing email with an encrypted attachment; FIG. 13 is an explanatory diagram showing an example of the structure of a notification email (for sender); FIG. 13 is an explanatory diagram showing an example of the structure of a notification email (for a destination). FIG. 11 is an explanatory diagram illustrating an example of the configuration of a discard request email. FIG. 11 is a sequence diagram showing a sending mail control operation. FIG. 11 is a sequence diagram showing an operation of sending a discard request email.

Next, an embodiment of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiment described below.

[Configuration of the mail control device]
An e-mail control device 10 according to the present embodiment will be described with reference to Fig. 1. Fig. 1 is a block diagram showing the configuration of the e-mail control device.

As shown in FIG. 1, the mail control device 10 is connected between the sender terminal 20 and the communication network NW, and is a device that controls the e-mails sent and received between the mail server 30 of the communication network NW and the sender terminal 20.

The sender terminal 20 is generally an information terminal such as a PC, tablet, or smartphone, and is connected to the mail control device 10 via a wired or wireless communication line L2. The sender terminal 20 has the function of sending and receiving e-mails using a mail application installed in the terminal in response to terminal operations.

The communication network NW is made up of a data communication network such as the Internet, and is connected to a mail server 30 that stores and distributes e-mails, and destination terminals #B, #C, and #D (40) that exchange e-mails with the source terminal #A (20).

When the mail control device 10 of this embodiment receives an outgoing mail including an attachment from the sending terminal 20, it automatically generates a password to encrypt the attachment, and sends the outgoing mail with the encrypted file attached to the destination terminal 40. The mail control device 10 creates a password notification mail (for the sender) including the encryption password for decrypting the encrypted file, and further creates a password notification mail (for the recipient) with the destination address of the outgoing mail set to the destination address of the password notification mail (for the sender), and sends it to the sending terminal 20.

When the sending terminal receives a password notification email (for the recipient) from the email control device 10, it checks the destination address of the outgoing email and the destination address of the password notification email (for the recipient) and sends it to the email control device 10.

At this point, a password notification email (for the recipient) containing the destination address of the outgoing email is sent to the sending terminal 20, so the sending terminal 20 can send the password notification email (for the recipient) simply by replying to the password notification email (for the recipient). This reduces the workload involved in creating the password notification email (for the recipient). Furthermore, if there is an error in the destination address of the original outgoing email, the incorrect destination can be deleted from the destination address of the password outgoing email (for the recipient) when sending the password notification email (for the recipient), thereby preventing the password notification email from being sent to the destination address that erroneously sent the outgoing email.

In this embodiment, a password notification email containing the destination address of the outgoing email is sent to the source terminal 20, and the password notification email is sent to the destination address of the password notification email received from the source terminal 20. This configuration reduces the workload on the source terminal 20, and provides a mail control device that can handle cases where the source terminal 20 has an error in the destination of the outgoing email.

[Configuration of the mail control device]
As shown in FIG. 1, the mail control device 10 mainly comprises a network interface unit (hereinafter referred to as network I/F unit) 11, a terminal interface unit (hereinafter referred to as terminal I/F unit) 12, a memory unit 13, and a control unit 14.

The network I/F unit 11 is a processing unit that transmits and receives various data, such as e-mail-related protocol messages and mail data, between the communication network NW via a wired or wireless communication line L1.

The terminal I/F unit 12 is a processing unit that transmits and receives various data, such as protocol messages and mail data related to e-mail, between the source terminal 20 and the terminal 20 via a wired or wireless communication line L2.

The memory unit 13 is a processing unit that consists of a storage device such as a hard disk or semiconductor memory, and stores various processing data and programs 13P used for mail control processing in the mail control device 10.

Program 13P is a mail control program that realizes various processing units for executing mail control processing by working in cooperation with the CPU of the control unit 14, and is read from an external device or recording medium (neither shown) connected to the mail control device 10 and is stored in advance in the memory unit 13.

[Control unit]
The control unit 14 includes a CPU (central processing unit) and its peripheral units, and realizes various processing units for executing the mail control process by reading out the mail control program from the storage unit 13 and executing it.

The main processing units realized by the control unit 14 are an email processing unit 14A, a password notification processing unit 14B, and an encryption processing unit 14C. These processing units are configured to perform the functions described below, but the relationship between these processing units and functions is not limited to the contents described below, and specific functions may be realized by other processing units.

[Mail processing section]
The mail processing unit 14A has the function of exchanging sent and received mail with the mail server 30 via the communication network NW, the communication line L1, and the network I/F unit 11, the function of exchanging sent and received mail with the sending terminal 20 via the communication line L2 and the terminal I/F unit 12, the function of relaying and forwarding sent mail from the sending terminal 20 to the mail server 30, and the function of relaying and forwarding received mail from the mail server 30 to the sending terminal 20.

In addition, when an attachment is attached to an outgoing email from the sending terminal 20, the email processing unit 14A has the functions of temporarily storing the outgoing email, with the attachment encrypted by the encryption processing unit 14C, in the memory unit 13 as a saved email 13A, sending the outgoing email to the email server 30, sending a password notification email (for the sender) including the encrypted password created by the password notification processing unit 14B to the email server 30, and creating a password notification email (for the recipient) that lists the destination address of the outgoing email in the destination address of the password notification email (for the sender) received from the email server 30, and sending the password notification email to the sending terminal 20.

The mail processing unit 14A also has a function of relaying the password notification mail (for destination) sent from the source terminal 20 to the mail server 30 after being confirmed at the source terminal 20. If necessary, the mail processing unit 14A can also have a function of acquiring the sent mail of the stored mail 13A in the memory unit 13, and a function of comparing the destination address of the password notification mail (for destination) with the destination address of the sent mail, creating a discard request mail with a specific destination address that does not exist in the password notification mail as the destination, and sending the mail to the mail server 30.

[Password notification processing section]
The password notification processing section 14B has a function of creating a password notification mail (for the sender) including the encryption password used in the encryption processing section 14C for encrypting the attached file.

[Encryption Processing Unit]
The encryption processing unit 14C has a function of generating an encryption password to be used for encrypting the attachment when the email processing unit 14A receives an outgoing email with an attachment from the sending terminal 20, a function of encrypting the attachment included in the outgoing email based on the generated encryption password, and a function of sending the encrypted file resulting from encrypting the attachment to the email processing unit 14A.

[Outgoing Mail Configuration]
Fig. 2 is an explanatory diagram showing an example of the structure of an outgoing email. As shown in Fig. 2, an outgoing email is composed of various items such as a sender address (From), a destination address (To, Cc), a subject, and an email body, and data indicating the contents. In this example, "[email protected]" is specified as the sender address, and two addresses "[email protected]" and "[email protected]" are specified as the destination addresses.

In addition, important confidential information and other content that is inappropriate to include in the body of the email is stored in a separate electronic file on the sender terminal 20 and attached as an attachment to the outgoing email. In the example of FIG. 2, an attachment with the file name "xxxxxx.doc" is attached to the outgoing email. Specific examples of attachments include document files and drawing files created on a PC, or photo files taken with a camera. This attachment is encrypted with a password automatically generated by the control unit 14, and the outgoing email with the encrypted attachment is sent to the mail server 30.

[Outgoing mail (encryption) configuration]
Fig. 3 is an explanatory diagram showing an example of the structure of an outgoing mail with an encrypted attachment. As shown in Fig. 3, an outgoing mail with an encrypted attachment is composed of various items such as a sender address (From), a destination address (To, Cc), a subject, and a mail body, and data showing the contents. The stored mail 13A in the storage unit 13 is an outgoing mail with an encrypted attachment.

In this example, the attachment is replaced with an encrypted file (compressed file) encrypted by encryption processing unit 14C, and the file name is changed to the encrypted file name "xxxxxx.zip". Also, as in FIG. 2, "[email protected]" is specified as the source address, and two addresses "[email protected]" and "[email protected]" are specified as the destination addresses.

[Password notification email (sender) configuration]
Fig. 4 is an explanatory diagram showing an example of the configuration of a password notification email (for sender). As shown in Fig. 4, a password notification email (for sender) is composed of various items such as a sender address (From), a destination address (To, Cc), a subject, and an email body, and data showing the contents. In this example, "[email protected]", which is the sender address of the outgoing email, is specified as the sender address, and "[email protected]", which is the same as the sender address, is written as the destination address.

The subject line also reads "Password notification email (for sender)," making it clear that the email is a password notification email for the sender to notify the sender's device of the password.

The email text also contains an explanation of the sender's password notification email, the password to be sent in this password notification email (for the sender), and details of the sent email to identify the sent email. In the example of Figure 4, the contents of the sent email sent from the sender address "[email protected]" to the destination addresses "[email protected]" and "[email protected]" are listed.

[Password notification email (for recipient)]
In this embodiment, a password notification mail (for destination) in which the destination address of the outgoing mail is written in the destination address of the password notification mail (for sender) in FIG.

In this embodiment, a separate password is generated for each outgoing email and is used commonly for multiple destination addresses included in the outgoing email, but this is not limited to the above. For example, to increase the security of attachments, a separate password may be generated for each destination address included in the outgoing email.

Figure 5 is an explanatory diagram showing an example of the structure of a password notification email (for recipient). As shown in Figure 5, a password notification email (for recipient) is composed of various items such as the sender address (From), the destination address (To, Cc), the subject, the email body, etc., and data indicating the contents. In this example, "[email protected]", which is the sender of the password notification email (for recipient), is specified as the sender address, and "To: [email protected]" and "Cc: [email protected]", which are the destinations of the original sent email, are specified as the destination addresses.

The subject line also reads "Password notification email (for recipient)," making it clear that the email is a password notification email for the recipient to notify the password of the destination device of the outgoing email.

The email body also contains an explanation about the password notification email for the recipient, the password to be sent in this password notification email (for the recipient), and details about the sending email to identify the sent email.

On the sender terminal 20 that receives this password notification email (for recipient), the sender can confirm the destination address specified in the sent email by checking the contents of the sent email described in the body of FIG. 5. As a result, if there is no error in the destination address of the sent email, the password notification email (for recipient) can be sent simply by replying to the password notification email (for recipient). This reduces the workload of creating the password notification email (for recipient).

On the other hand, if the destination address of the outgoing email is incorrect, the incorrect destination address in the password notification email (destination) can be deleted, so that the password notification email (for destination) can be sent only to the correct destination. This means that the password notification email (for destination) will be sent from the email control device 10 only to the correct destination address specified in the password notification email (for destination) from the sender terminal 20.

For example, in FIG. 5, if the destination address "To: [email protected]" is an incorrect destination address and the destination address "Cc: [email protected]" is the correct destination address, then by deleting "To: [email protected]" from the sending address of the password notification email (for the recipient), it is possible to prevent the password notification email (for the recipient) from being sent to the incorrect destination address.

[Operation of the mail control device according to this embodiment]
The operation of the mail control device 10 according to the present embodiment will be described with reference to Fig. 7. Fig. 7 is a sequence diagram showing the outgoing mail control operation. The mail control program stored in program 13P causes the mail control device 10 to execute each step in the following sequence.

When sender terminal #A creates an email with an attachment (step S100) and performs a send operation (step S101), the email is sent from sender terminal #A to the email control device 10 (step S102).

The mail processing unit 14A of the mail control device 10 receives an outgoing mail with an attachment in response to a mail sending request from sender terminal #A. In the example of FIG. 2, the sender address of the outgoing mail is "[email protected]", the destination addresses are "[email protected]" and "[email protected]", and the file attached is "xxxxxx.doc".

The encryption processing unit 14C generates an encryption password to be used to encrypt the attachment for each outgoing email received by the email processing unit 14A (step S103). In the example of FIG. 4, the encryption password "hagr21vas" is generated.

The encryption processing unit 14C encrypts the attached file using the generated encryption password (encryption step) (step S104), and the mail processing unit 14A sends the outgoing mail with the encrypted file attached to the mail server (step S105). The mail processing unit 14A stores the outgoing mail as saved mail 13A in the memory unit 13 (save step) (step S106). In the example of FIG. 3, the outgoing mail with the encrypted file "xxxxxx.zip", which is the encrypted file "xxxxxx.doc", attached is sent and saved.

The password notification processing unit 14B creates a password notification email (for sender) as shown in FIG. 4 as an email to notify the sender terminal #A of the encryption password used to encrypt the attachment (step S107), and the email processing unit 14A sends this password notification email (for sender) to the email server via the network I/F unit 11, communication line L1, and communication network NW (step S108).

Then, the mail processing unit 14A receives a password notification mail (for sender) from the mail server 30 via the communication network NW, the communication line L1 and the network I/F unit 11, creates a password notification mail (for recipient) in which the destination address of the sent mail is written to the destination address of the password notification mail (for sender) (step S109), and sends it to the sender terminal #A via the terminal I/F unit 12 and the communication line L2 (notification step) (step S110).

The sender terminal #A checks the password notification email (for the recipient) received from the email control device 10 (step S111), and based on the contents of the body of the password notification email, checks the password generated by the email control device 10 and checks the recipient address specified in the outgoing email.

After confirming the destination of the password notification email (for recipient), sender terminal #A sends a reply to the password notification email (for recipient) to the correct destination address (step S112).

When the mail control device 10 receives a password notification mail (for the destination) from the sender terminal #A (step S113), it relays the received password notification mail (for the destination) to the mail server (step S114).

Destination terminals #B and #C receive the password notification email (for the destination) from sender terminal #A via mail server 30, and based on the password stated in the password notification email (for the destination), can decrypt (unzip) the attachment attached to the sent email and open the original attachment.

If the destination address of the outgoing email is incorrect, the incorrect destination address in the password notification email (destination) can be deleted, so that the password notification email (for destination) can be sent only to the correct destination. This means that the password notification email (for destination) will be sent from the email control device 10 only to the correct destination address specified in the password notification email (for destination) from the sender terminal 20.

For example, in the example of FIG. 5, if the destination address "To: [email protected]" is an incorrect destination address, "To: [email protected]" can be deleted from the sending address of the password notification email (for recipient) to prevent the password notification email (for recipient) from being sent to the incorrect destination address.

[Disposal request email sending behavior]
The mail processing unit 14A may be configured to compare the destination address of the password notification mail (for destination) received from the source terminal 20 with the destination address of the original outgoing mail, and to send a mail requesting the destruction of the outgoing mail to a specific destination address that is in the destination of the outgoing mail but is not in the destination of the password notification mail (for destination). Fig. 8 is a sequence diagram showing the operation of sending the destruction request mail.

In the example of FIG. 5, if the destination address "Cc:[email protected]" is the correct destination and the destination address "To:[email protected]" is an incorrect destination, the destination address "[email protected]" is deleted from sender terminal #A, and a password notification email (for the destination) is sent with the destination address "Cc:[email protected]" (step 112).

When the email processing unit 14A receives a password notification email (for the destination) from the sender terminal #A (step S113), it relays the received password notification email (for the destination) to the email server (step S114).

Destination terminal #C receives the password notification email (for the destination) from sender terminal #A via mail server 30, and based on the password stated in the password notification email (for the destination), can decrypt (unzip) the attachment attached to the outgoing mail and open the original attachment. On the other hand, destination terminal #B cannot receive the password notification email (for the destination) from sender terminal #A via mail server 30, and therefore cannot decrypt (unzip) the attachment attached to the outgoing mail.

The email processing unit 14A further retrieves the outgoing email corresponding to the password notification email (for the destination) from the stored email 13A in the memory unit 13, and compares the password notification email (for the destination) with the destination address of the outgoing email (comparison step) (step S120).

If the comparison shows that the destination address of the outgoing email contains a specific destination address that does not exist in the password notification email (for destination), a discard request email is created with that destination address as the destination (step S121) and is sent to the mail server 30 (sending step) (step S122).

When the destination address of the password notification email (for destination) (Figure 5) is compared with the destination address of the outgoing email (Figure 3), if the destination address of the outgoing email contains the destination address "[email protected]" that does not exist in the password notification email (for destination), the destination address of the discard request email will be the destination address "To:[email protected]" to which the outgoing email was sent in error. The discard request email will be sent from the email control device to the email server 30 and then to the destination terminal #B.

Regarding "[email protected]" specified as the destination address in the outgoing email, if the sending terminal realizes that it was sent erroneously and does not send a password notification email from sending terminal #A, the email control device 10 will not send a password notification email to the destination address "[email protected]". Instead, the email control device 10 will send a discard request email to the erroneous destination "[email protected]".

[Configuration of the deletion request email]
Fig. 6 shows an example of the structure of a discard request email. As shown in Fig. 6, the discard request email is composed of various items such as a sender address (From), a destination address (To), a subject, and an email body, and data indicating the contents of the items.

The subject of the email reads "Deletion Request Email," making it clear that the email is an email to request the destination device to delete the email. The body of the email contains an explanation that the email was sent by mistake and provides details about the email.

In this example, a comparison of the destination address of the password notification email (for destination) (Figure 5) with the destination address of the outgoing email (Figure 3) reveals that the destination address of the outgoing email is "[email protected]", which does not exist in the password notification email (for destination), so the destination address of the discard request email is "To:[email protected]", the destination address to which the outgoing email was sent in error. The discard request email is sent from the email control device 10 to the email server 30, and then to the destination terminal 40 corresponding to that destination address.

In FIG. 6, an example is described in which the destination address of the outgoing email contains one specific destination address that does not exist in the password notification email (for destination). Even if there are multiple specific destination addresses, multiple discard request emails containing one specific destination address may be created, or a discard request email containing multiple specific destination addresses may be created.

In FIG. 8, the mail control device creates a discard request email and sends it to the erroneously sent destination address. However, the discard request email may be sent to the sending terminal before sending, and may be sent after the sending terminal confirms the contents and sending of the discard request email.

The email control device may also notify the sending terminal of the result of sending the discard request email, or may send the discard request email to the sending terminal and the destination terminal of a specific destination address.

[Effects of this embodiment]
In this way, in this embodiment, a password notification email containing the destination address of the outgoing email is sent to the sending terminal to the destination address of the password notification email, and the password notification email is sent to the destination address of the password notification email received from the sending terminal.This reduces the workload on the sending terminal and provides an email control device that can respond if there is an error in the destination of the outgoing email at the sending terminal.

In addition, by comparing the destinations of the outgoing email and the password notification email, and configuring it to send a discard request email to any destination of the outgoing email that does not exist in the password notification email, if there is an error in the destination of the outgoing email, the sending terminal will not need to create and send the discard request email, making it possible to reduce the workload on the sending terminal.

[Extended embodiments]
Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above-mentioned embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. In addition, the respective embodiments can be implemented in any combination within a range that does not contradict each other.

10...mail control device, 11...network interface unit (network I/F unit), 12...terminal interface unit (terminal I/F unit), 13...storage unit, 13A...stored mail, 13P...program, 14...control unit, 14A...mail processing unit, 14B...password notification processing unit, 14C...encryption processing unit, 20...sender terminal, 30...mail server, 40...destination terminal, L1, L2...communication line, NW...communication network.

Claims (6)

In a mail control device, when a file is attached to an email sent from a sending terminal, the attached file is encrypted and sent to a destination terminal,
an encryption processing unit that encrypts the attached file;
a mail processing unit that transmits the outgoing mail with the encrypted attachment to the destination terminal;
a storage unit for storing the outgoing email with the encrypted attachment;
a password notification processing unit that creates a password notification email including an encryption password for decrypting the encrypted attachment;
The mail processing unit includes:
an email control device that sends the password notification email to the sending terminal, with the destination address of the sent email stored in the memory unit written in the destination address of the password notification email, receives the password notification email returned from the sending terminal, and sends the password notification email to the destination address of the password notification email received from the sending terminal. The mail processing unit includes:
2. An email control device as described in claim 1, which compares the destination address of the password notification email received from the sending terminal with the destination address of the outgoing email stored in the memory unit, creates an email requesting the discarding of the outgoing email to be sent to a specific destination address that is the destination of the outgoing email and is not the destination of the password notification email, and creates a discard request email containing one of the specific destination addresses or multiple of the specific destination addresses, and sends the discard request email to the destination terminal of the specific destination address. The mail processing unit includes:
3. The mail control device according to claim 2, further comprising: a mail control unit that transmits the discard request mail to the transmission source terminal; and, after the transmission of the discard request mail is confirmed by the transmission source terminal, transmits the discard request mail to a destination terminal of the specific destination address. 4. The mail control device according to claim 2, wherein the mail processing unit notifies the sending terminal of a result of sending the discard request mail. 5. The mail control device according to claim 2, wherein the mail processing unit transmits the discard request mail to a destination terminal of the specific destination address and to the source terminal. A mail control program executed in a mail control device that encrypts an attached file and transmits the file to a destination terminal when a file is attached to an outgoing mail from a source terminal,
an encryption step of encrypting the attachment;
sending the outgoing mail with the encrypted attachment to the destination terminal;
a storage step of storing the transmitted email with the encrypted attachment;
creating a password notification email including an encryption password for decrypting the encrypted attachment;
a sending step of sending the password notification mail to a destination address of the password notification mail received from the sender terminal;
a step of sending the password notification mail to the sender terminal, the password notification mail including the destination address of the sent mail stored in the storing step described above as a destination address of the password notification mail;
receiving the password notification email returned from the sender terminal;
a sending step of sending the password notification mail to a destination address of the password notification mail received from the sending terminal.

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