I've been trying to get this to work all day. Outgoing and incoming email servers both work. My domain alias is set to the same as the mail server, my user alias is set to same user as the outgoing/incoming mail server. catchall was set to catchall, which caused emails to fail as they were being sent from "company" catchall@domain.com which isn't an authorized user of the outgoing smtp address. I tried seting catchall alias to the same as my email alias and now it has the same error but appears to be sending from postmaster-odoo@domain.com. wtf... So I set the bounce alias the same as my user alias and it failed with the same error as it added numbers to the back of the alias: alias-23@domain.com.

The only authorized user is alias@domain.com, and if they are not being sent from alias@domain.com the email will fail. Why is this so hard?