subdomain mail problem

I am having a problem with a doamin which is an alias of another, the email is bouncing, and I have a mind-block at the moment

“The mail server responded: 5.1.1 Recipient address rejected: User unknown in virtual alias table.”

now I know this is an issue with perhaps the alias table that I need to add domain2 : domain1 as a pointer and update the table. I had a feeling this was in the ‘aliases’ table but I can’t seem to see anything there.

DNS works for the domain but subdomain email addresses are bouncing.

thanks for any advice

I think the issue may be to do with the /etc/postfix/virtual file

teh subdomain entry for this is not in there, so I manually added a new line

but sending email still isn’t working.