Then you talk "directly"  you alway talk about Postfix. Postfix can do it and i could make it directly. Iredmail-pro panel not , that's the question)

1. create user1@domain1.com as mailbox
2. edit user1@domain1.com alias field and try to add alias user2@domain2.com
not possible

it seems , that only possible way is create mailbox user2@domain2.com  and forward it to user1@domain1.com. but in this case user1@domain1.com can't send mails as user2@domain2.com until i remove restriction for ANY user to send email form ANY mailbox i have.

yes

Seems i misunderstood your request from beginning.

iRedAdmin-Pro restricts alias address in same domain. If you want to deliver emails sent to both user@domain1.com and user@domain2.com to same mailbox, another way is: use same maildir path -- you can update it in user profile page.

If you want to send email as user@domain2.com, you can allow user@domain1.com in /opt/iredapd/settings.py like this:

ALLOWED_LOGIN_MISMATCH_SENDERS = ['user@domain1.com']

But user@domain1.com will be able to send email as other addresses like 'user@domain3.com', 'user@domain4.com'.

Maybe we can improve this "ALLOWED_LOGIN_MISMATCH_SENDERS" setting by specifying allowed different senders like this:

ALLOWED_LOGIN_MISMATCH_SENDERS = [
    {'user@domain1.com': ['user@domain2.com']}
}

So that only "user@domain2.com" is allowed, not all addresses.

hmm, i din't know about this option.