Duplication of email when it contains the same address inside To, Cc and Bcc

[catap]

Let assume that I have a trivial email:

From: Kirill A. Korinsky <[email protected]>
To: [email protected]
Cc: [email protected]
Bcc: [email protected]
Subject: Test To, Cc and Bcc

which I delivery via OpenSMTPD 7.4.0 which triple (!) that email:

Jan 20 14:02:03 mx1 smtpd[15700]: 19a656ee3d6448e3 smtp connected address=[some IP] host=[some PTR]
Jan 20 14:02:04 mx1 smtpd[15700]: 19a656ee3d6448e3 smtp tls ciphers=TLSv1.3:TLS_AES_256_GCM_SHA384:256
Jan 20 14:02:04 mx1 smtpd[15700]: 19a656ee3d6448e3 smtp authentication [email protected] result=ok
Jan 20 14:02:04 mx1 smtpd[15700]: 19a656ee3d6448e3 smtp message msgid=a6f46d38 size=1615 nrcpt=3 proto=ESMTP
Jan 20 14:02:04 mx1 smtpd[15700]: 19a656ee3d6448e3 smtp envelope evpid=a6f46d3876398565 from=<[email protected]> to=<[email protected]>
Jan 20 14:02:04 mx1 smtpd[15700]: 19a656ee3d6448e3 smtp envelope evpid=a6f46d38ab15f1fe from=<[email protected]> to=<[email protected]>
Jan 20 14:02:04 mx1 smtpd[15700]: 19a656ee3d6448e3 smtp envelope evpid=a6f46d383ffc55b2 from=<[email protected]> to=<[email protected]>

Here I expect that MTA eliminates duplicated email addresses, and usually SMTPD does that.