What they see today is:
and the original message is attached (so they click on that to find out what the original "problem address" was).This is the mail system at host webmail.abc.com. I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below. For further assistance, please send mail to postmaster. If you do so, please include this problem report. You can delete your own text from the attached returned message. The mail system : connect to NAMEREDACTED.com[*****IP REDACTED*****]:25: Connection timed out.
What they'd like to see is failed recipient details in the body message.
This feels like it might be a postfix configuration, has anyone every considered doing something like this?