Suspect, mails are banned due to attachent only for single user.

[Damian]

All I can say is that the described behavior does not fit the config you
have posted. Your description sounds like some banned_*_maps are
involved at some point, maybe even indirectly via inclusion of other
config files.

> I'm pretty shure to have the right part of the debian config files. We have some adoptions in the files located at /etc/amavis/conf.d
>
> Some initial settings are in 20-debian-default and the part copied in was from file 90-local-settings, which will be the last loaded while starting.
>
> The funny thing is, the same sender can submit the same mail with identical attachement to other recipients with no problems.
>
> I saw 1 mail to multiple recipient, for witch exacly the mail for exacly the one recipient was banned.