How can I query postfix to test is an address is in the virtual address file?
How about postalias:
postalias -q [email protected] /path/to/your/valias_file
sendmail -bv [email protected]
Despite the name, this is a Postfix program. This will deliver an email to the caller's mail account that will give you the information about full address resolution. The command-line output is typically just:
Mail Delivery Status Report will be mailed to <yourusername>.
postalias -q will show you what the alias file has in it, as the previous responder said, but this may or may not be what actually happens; sendmail -bv is more complete.