Is the mail_alias table used anywhere? Mail aliases are actually saved in mail_forwarding (with type='alias'). I'm guessing maybe it's old cruft which could be removed?
The ispconfig3.sql file has no mail_alias table as far as I can see. Either its a very old remnant table that was removed from ispconfig source already or it was created by an addon or so that you use?
Ok, well, I have no idea where 'mail_alias' even came from now, I don't even find it on the servers I'm using, though I thought I was querying against it prior to posting.... who knows, I probably just got mixed up with remote api calls ('mail_alias_get' does not get from the 'mail_alias' table), sorry for the noise.