Emails on Site Names With Commas Are Bounced by Google

Thanks, this confirmed the same problem for me of email sent to gmail from a site name with an apostrophe.

This error not only seems to occur with commas. When a site name contains ", ' or < followed by >, it also isn't allowed.
We should add quotes around the name and escape double quotes.

I have added a patch which escapes double quotes. I have also updated the test.

Rerolled patch as it no longer applies on 8.4

Patch rerolled.

I am not sure this is the right fix, as shown by the tests this would appear to corrupt MIME encoded headers - according to the spec it looks like these should not be quoted. http://www.rfc-editor.org/rfc/rfc2047.txt says

+ An 'encoded-word' MUST NOT appear within a 'quoted-string'.

We can either special-case the result of Unicode::mimeHeaderEncode when it comes back unchanged but the string still contains unwanted characters, or maybe Unicode::mimeHeaderEncode needs extending to consider encoding the unwanted characters as well. Right now it assumes the entire ASCII set is valid.

This bug got me on two D8 installs with commas in the sitename.

#10 / longwave made the point of where to fix the issue.

1) Within Unicode::mimeHeaderEncode()
or
2) Within MailManager doMail()

RFC2047 is focused on "textual header information in character sets other than US-ASCII" and the MIME standards all seem to address non-ASCII formats so tampering with mimeHeaderEncode() seems inappropriate since the method and the RFC it references are geared to non-ASCII. So, this would mean a fix that involves doMail().

Should we do a variation of longwave's suggestion

$encoded_site_name = Unicode::mimeHeaderEncode($site_config->get('name'), TRUE);

// if the encoded site name contains only ASCII characters
if (preg_match('/[^\\x20-\\x7E]/', $encoded_site_name)) {
    // wrap the ASCII in double-quotes to account for special ASCII characters, like commmas
    $encoded_site_name = '"' . addcslashes($encoded_site_name, '"') . '"';
}

$headers['From'] =  $encoded_site_name. ' <' . $site_mail . '>';

or a variation

$encoded_site_name = Unicode::mimeHeaderEncode($site_config->get('name'), TRUE);

// if the encoded site name matches the original value then it contains only ASCII characters
if ( $site_config->get('name') == $encoded_site_name)
{
    // wrap the ASCII in double-quotes to account for special ASCII characters, like commas
    $encoded_site_name = '"' . addcslashes($encoded_site_name, '"') . '"';
}

$headers['From'] =  $encoded_site_name. ' <' . $site_mail . '>';

This also begs the question of if the $reply variable in doMail() also needs to get the same treatment as the From because Reply-To also allows for a name portion before the email address.

This issue isn't limited to just Google/Gmail. Any RFC valid email receiver would have the issue.

Closing this as a duplicate since more recent conversations were had on an issue that's tagged as Major and "mail system"
https://www.drupal.org/project/drupal/issues/2745039