Recipient domains mangled for mailing lists

[ScratchMonkey]

When I send to mulberry-dev@lists.mulberrymail.com, the "lists." part is getting stripped before the receiving server sees it, so the mail can't be delivered, and I get a bounce. The copy of the message in the bounce has been mangled to change "lists.mulberrymail.com" in the To: field to just "mulberrymail.com" and the receiving server says "no such user". (It's a different virtual mail server, so that's expected!) I can see the correct recipient domain in the envelope address in my outbound mail server log when it connects to smtp.comcast.net. So it looks like the Comcast server is changing that and rendering the message undeliverable. 

[ScratchMonkey · Accepted solution]

Spoiler

Solved. This turned out to be a configuration error on the mailing list. The mailing list admin fixed it. He was using a DNS CNAME for his mailing list server name, and mail server programs are allowed to replace the right-hand side of a destination address with the CNAME's real name. The list's "real" server was set up to accept only email for the list's server name, not the real server name. The rule is to never use a CNAME for your mail server. Only use an "A" record.

More info here:

https://cr.yp.to/im/cname.html