With iRedAdmin-Pro, domain alias "domainA.com -> domainB.com" will add user alias to all users under domainB.com, so:
user2@domainB.com will have a user alias: user2@domainA.com, NOT 'user1@domainA.com' by default.

You have to add "user1@domainA.com" in user alias page manually. like below:

No.

Just add an alias domain name, and that's it.
As i mentioned above, domain alias "domainA.com -> domainB.com" will add user alias to all users under domainB.com automatically, so:
user2@domainB.com will have a user alias: user2@domainA.com.

All users under domain domainB.com will have another email address, with same username and '@domainA.com'.
user01@B.com => user01@A.com
user02@B.com => user02@A.com

But you says you want different username with alias domain (a typo error), user02@B.com => user01@A.com.
user02@B.com will have another address "user02@A.com", so you have to add "user01@A.com" manually.

That's easy.

Steps with iRedAdmin-Pro:

- Create domain B.com.
- Create all accounts with same username as A.com. For example, if you have "user01@A.com", then create "user01@B.com" with iRedAdmin-Pro.
- In domain list page, click the gear icon at the right side of domain name "B.com" to edit profile.
- Switch to "Aliases" tab in domain profile page. Here's  screenshot.
- Add "A.com" and click "Save changes".

That's all.

For MySQL backend, add it in vmail.alias_domain.
For OpenLDAP backend, add domain name in attribute "domainAliasName" of domain object.

Dear kevothi,

First of all, please always create a new forum topic for your own question, do not hijack other's thread.

Alias domain requires more work than adding 'domainAliasName' in domain object, you must add 'shadowAddress=[username]@[alias_domain' for all mail users/lists/aliases too.