Email bouncing "User unknown in virtual alias table"

I keep getting the following message in my maillog:

“postfix/trivial-rewrite[31990]: warning: do not list domain (mydomain.com) in BOTH mydestination and virtual_alias_domains”

So I tried going into /etc/postfix/main.cf and I put:

mydestination =

I then restart postfix and try to send an email and bounces back, the error in maillog is:

postfix/error[32107]: C827415E49EF: to=username-mydomain.com@mydomain.com, orig_to=username@mydomain.com, relay=none, delay=0.16, delays=0.15/0/0/0, dsn=5.0.0, status=bounced (User unknown in virtual alias table)

My /etc/postfix/virtual file has:

mydomain.com mydomain.com

user@mydomain.com user-mydomain.com

Any idea whats wrong with my postfix virtual file? I set everything up in the virtualmin control panel (no manual modifications to the virtual file). If I comment out “mydestination =” I get my emails, but also those warning emails in my log (which i’d like to stop)