[HOTFIX] fix missing ListID introduced with with Mail Team egroup migration tool
To identify the source egroup and the dest channel and permissions, ListID header + Delivered-To headrs were both required and used. The Mail Team egroup to channel migration tool is removing delivery to Exchange groups and delivers directly to a contact, so ListID header is missing. Delivered-To header is hopefully still there thanks to sieve rule we added in dovecot.
HOTFIX will try to process anyway despite the lack of ListID, let's hope it will cover all scenarios.