email sub-addressing/tagging - user+tag@example.hr as "Email aliases" not working

When I try to add an email alias with tags I cannot confirm it because the conformation email never arrives.

I checked with my mail provider and they are supported now (not by default).
I tried sending email to my user+tag@domain.hr account and mail has been received OK (sent from gmail.com).

Update: it is working on user+tag@domain.net but not on user+tag@domain.hr.