 <p>Catch-all email trappers aren't implemented in DNS to the best of my knowledge, they're configured at the email server level. So there's no shortcut for testing this other than checking for the validity of an email address.</p> <p>Note that you don't have to actually send an email to test. Within, say, an SMTP session the RCPT TO command returns: 200 or 250 on success, 251 or 551 on forward, 252 cannot verify but will accept, 450 or 550 mailbox unavailable, 552 exceeded storage, 553 mailbox name not allowed. Upon determining whether/not the wildcard exists you'd send a QUIT.</p>