Postfix wont send mail to external email addresses listed in virtual_alias_domains

General information for the business: Development
Description of requirements/functionality: We have our main server at mail.mainserver.com with the catchall address catch@mail.mainserver.com

We also have two other domains: domain1.com and domain2.com which are hosted at gmail. Gmail is re-routing catchall emails to catch@mainserver.com

In /etc/postfix/main.cf

virtual_alias_domains = domain1.com, domain2.com
virtual_alias_maps = hash:/etc/postfix/virtual
And in /etc/postfix/virtual

@mail.mainserver.com catch@mail.mainserver.com
@domain1.com catch@mail.mainserver.com
@domian2.com catch@mail.mainserver.com
These settings are working when it comes to receiving email to either of the above domains, but the issue we are having is in sending an email from a virtual alias ie testoutgoing@mail.mainserver.com to an existing mailbox at gmail ie existing@domain1.com

The email is not sent, instead it is placed into the inbox of catch@mail.mainserver.com

Is there any way to create an ignore list, so that postfix ignores checks on the virtual alias table for specific email addresses and sends them as it would to any other external email address?

Thanks in advance.
Specific technologies required: postfix, linux, smtp, email
OS requirements: Linux
Extra notes: