List-Unsubscribe & List-Id header values should not be encoded

[ferraro]

Problem description

List-Unsubscribe & List-Id header values should not be encoded

Values will be encoded, mail clients like Apple Mail are unable than to read the values for the unsubscribe button.

Code to reproduce

$mail->addCustomHeader('List-Unsubscribe', "<mailto:...>");
$mail->addCustomHeader('List-Id', "123.list-id.".domain.tld>");

Debug output

List-Unsubscribe: =?us-ascii?Q?<mailto:unsubscribe=5Fstatus=5Freport\@api-dev.?=
 =?us-ascii?Q?trashmail.com=3Fsubject=3Did%3Dbe1115d2-a845-4f?=
 =?us-ascii?Q?c0-b5fa-f29c578f84ba>,_<https://dev.trashmail.c?=
 =?us-ascii?Q?om/=3Fcmd=3Dunsubscribe=5Fstatus=5Freport&id=3D?=
 =?us-ascii?Q?be1115d2-a845-4fc0-b5fa-f29c578f84ba>?=
List-Id: =?us-ascii?Q?be1115d2-a845-4fc0-b5fa-f29c578f84ba.list-id.de?=
 =?us-ascii?Q?v.trashmail.com>?=

[Synchro]

Oddly, this behaviour in PHPMailer originated by copying exactly what Apple Mail does with long lines! This is standard RFC2047 encoding, and it's the only way you can wrap lines without introducing extra spaces when it's decoded. What other solution do you have for that?

[Synchro]

The best workaround for this is to use SMTP to localhost instead of mail(), so add a call to isSMTP() to your code. This encoding is only done in order to avoid a bug in mail(), and although it's entirely RFC compliant, some email clients don't like it.