[DRE-maint] Bug#948981: schleuder: fails to gracefully handle incoming mails which are not encrypted to the list key

[Georg Faerber]

Package: schleuder
Version: 3.4.1-1
Forwarded: https://0xacab.org/schleuder/schleuder/issues/337 
Tags: fixed-upstream

Schleuder fails to handle incoming mails, which are not encrypted to the
list key, but are encrypted to a different key, using symmetric
encryption or are just containing PGP-garbage. It throws an exception
and errors out.

A fix addressing this issue was released upstream: Don't throw an
exception, don't notify (and annoy) the admins, instead inform the
sender of the mail how to do better.