IDN E-mail with username in Unicode is not accepted

[rosmanov]

Validation fails, if the E-mail username contains non-ASCII characters:

<?php
$m = new PHPMailer();
$m->CharSet = 'utf-8';
$m->ContentType = 'text/html';
$m->Encoding = 'base64';

$e = 'османов@письмо.рф';
$ep = $m->punyencodeAddress($e);
var_dump($ep);
var_dump($m->validateAddress($ep, 'pcre8'));

Actual output:

string(37) "османов@xn--h1aigbl0e.xn--p1ai"
bool(false)

Expected output:

string(37) "османов@xn--h1aigbl0e.xn--p1ai"
bool(true)

[Synchro]

This is intentional, and mentioned in #88. UTF-8 in the local part of email adresses is only supported via RFC6531, and that has very little adoption as yet (pretty much only gmail). What's more of a problem is that if you use such an address and then try to send it via a server which doesn't support it, you're stuck with having to do everything in RFC6857, which really isn't pretty and requires architectural changes (because a message cannot be rendered until after you have connected to the server). As part of that process, punycode can be applied to the local part of addresses via RFC5891 and RFC5890, but support for that is even worse than for RFC6531.

In the absence of that support, we are back to RFC5321's definition of an email address, in which the address you're trying to use is not valid, as the validate function says.

In short, doing this is an enormous amount of work, so if you feel like writing it and doing a PR, be my guest.

[UA2018]

The Universal Acceptance Steering Group (UASG), supported by the Internet Corporation for Assigned Names and Numbers (ICANN), is a community-led, industry-wide initiative working on creating awareness and identifying and resolving problems associated with the universal acceptance of domain names. The purpose of these efforts is to help ensure a consistent and positive experience for Internet users globally.

You may find the following information useful in developing systems, internet applications that accept IDNs, EAI and New gTLDs.

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https://uasg.tech/wp-content/uploads/documents/UASG005-en-digital.pdf

Good Practice Recommendations:
https://uasg.tech/wp-content/uploads/documents/UASG007-en-digital.pdf

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