The MIME type multipart/mixed is used for the mail messages used in mail.cgi, wio-lib.pl and acct.pl Clients such as Thunderbird, Outlook and Roundcube look at the Content-Type multipart/mixed and treat this as meaning that an attachment is provided even when there is no Disposition attachment in the email source. RFC1341 does not indicate that multipart/mixed means an attachment is attached, only that there are different sections containing different content types. Therefore the use of multipart/mixed in IPFire is not incorrect but in many email clients it results in messages being flagged as having attachments when they don't.
acct.pl sends a pdf attachment with its messages therefore this must stay with multipart/mixed. mail.cgi and wio-lib.pl only send a single text message with no attachments or separate sections of different content. These two usages, if changed to multipart/alternative stop Thunderbird or Roundcube from showing the attachment icon with those messages. I have tested this change out and confirmed that changing from multipart/mixed to multipart/alternativce for these two usages fixes the problem of the attachment icon being shown in Thunderbird or Roundcube.
Oh sorry for being too fast with assigning this to someone :)
Bug fix created and tested out. Changed multipart/mixed to multipart/alternative in mail.cgi and wio-lib.pl Patches submitted to dev mailing list and patchwork. https://lists.ipfire.org/pipermail/development/2023-February/015469.html https://lists.ipfire.org/pipermail/development/2023-February/015470.html https://patchwork.ipfire.org/project/ipfire/list/?series=3408
Thank you very much for these! https://git.ipfire.org/?p=ipfire-2.x.git;a=commit;h=670981e64870b43981617560ce96b41db3a462fb https://git.ipfire.org/?p=ipfire-2.x.git;a=commit;h=c151ca241bfea1ea84b92269cd824971aabea732
https://blog.ipfire.org/post/ipfire-2-27-core-update-174-is-available-for-testing
This has been tested on my vm testbed with CU174 Testing. Sending a test email from the Mail Service page in the WUI no longer results in an attachment icon being shown for the message. This confirms that the bug has been fixed.
https://blog.ipfire.org/post/ipfire-2-27-core-update-174-released