[cobalt-users] Email users getting other user's email

["cobalt" <cobalt@xxxxxxxxxxxxx>]

I'm having a problem where mail sent to webmaster@xxxxxxxxxxx is received by webmaster@xxxxxxxxxxxx 
Both user1 and user2 have alias of webmaster (as well as several other users on the machine, but user2 only gets those sent to the domain of user1). user1 and user2 are completely unassociated with each other. They've never known each other and nutil now didn't know that each other's domains existed.
I tried wiping domain1.com and re-adding it via the web interface, but no dice. I tried adding the catch-all of @domain1.com as an alias to user1 but webmaster@xxxxxxxxxxx still goes to user2's email box.
I couldn't find anything in Cobalt knowledge base about this nor in the email achives of this list, that I searched. 
Any help would be appreciated.