email to a formerly add-on domain getting blocked?

[obdriftwood]

Ugh, not even sure if this is the right place to post this. Very complicated, will try and make it simple:
1. I host an email domain (domain A on server A) for a church and I have a Dadamail list set up for that domain.
2. Church has four domains and wants to switch them all to server (server B), someone starts setting up things in server B's cpanel using domain A as an add-on domain. Begins a mailman list at the same address as Dada list above. No nameservers are switched.
3. Church staff switch addresses to domain B (on server B), want all domain A addresses changed to forwarders (on server A).
4. Havoc ensues when server B thinks that it owns domain A (as it was set up as an add on). Nothing gets forwarded, all sorts of stuff dropped.
5. Delete add on domain A from server B. Forwarding issues clear up.
6. Attempt to post to Dadamail list from address on domain B. Receive immediate rejection messages from localhost mailman :-/
7. Server A&B tech support has little grasp on / interest in the problem.

Have I forgotten to clear out the add on domain A somewhere in server B's cpanel? I don't see it anywhere, but no other addresses are having this problem in Dada.

Any ideas would be appreciated.

 

[Infopro]

You might be able to track down any issues using a tool like this one:
/http://mxtoolbox.com/

 

[obdriftwood]

Thanks! Analyzing the header on that site clearly shows that the rejection email is from mailman on server B. Have you guys ever seen errors like this where the system thinks it owns a domain that it doesn't and causes email issues?

 

[Infopro]

Have you modified any of the settings in cPanel > Mail section > MX Entry?

 

[obdriftwood]

For some reason the cpanel still had a mailing list for the old domain still there, but hidden. The host support were able to find it and remove it (once they believed me that it was actually there). Thanks folks!