Today I tried to forward a message using the function "Forward as attachment". My mail service provider's server returned a message that it was not delivered because of:

<**hidden**@**hidden*>: host 127.0.0.1[127.0.0.1] said: 550 5.7.1 id=**hidden** -
    Rejected by next-hop MTA on relaying, from MTA(smtp:**hidden**): 550
    5.7.1 This message was recognized as spam by ********* infrastructure and
    is not delivered to the final recipient (in reply to end of DATA command)

Then I tried saving manually the message I wanted to fowrard in a txt file and attaching it. Then sending was successful.

Comparing the source of the two messages I noticed that in the first case, right after my signature the message continues with:

--***hidden***
Content-Type: message/rfc822
Content-Transfer-Encoding: binary
Content-Disposition: inline

and in the second case:

--***hidden***
Content-Type: text/plain
Content-Transfer-Encoding: quoted-printable
Content-Disposition: attachment; filename=message.txt

I suppose there are some rules which consider the first case spammy.


In case this is not a bug - please at least consider adding an option for fowrading with Content-Disposition: attachment.


Tested in version 3.17.3git194