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.
Thank you very much for these!
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.