Attachment remove/does not appear for external email

[MLaudren]

While trying to send a message with attachment, it correctly appear on the peps UI, but nothing on the recipient box.

Will provide further logs later.

[MLaudren]

Didn't find interesting logs about this...
No error in smtpin/smtpout or server.

[MLaudren]

@hbbio, does the PEPS teams still work on this repo or do we have to consider it as abandoned?