I know!I've never said it worked; only that it did no harm.
Yes. That is the problem.If not, is customerdomain.com a real domain name on your server. My code does not block mailer-daemon for non-existent users, only for non-existent domains.
The domain does exist, but the mailaddress does not. Mail is accepted, then the recipient does not exist and a bounce message is created.
This was no problem for years but since the backscatter problem is growing it is.
Don't know why it was not that clear to me sooner ;-)
I am staring at the exim.conf right now but I still look like chinese to me. But I am learning ;-)