I'm thinking this is really really super simple, but I can't figure out what I need to do. I don't mess with Postfix much (Just let it run and do its thing) so I've got no idea where to even start with this.

We have postfix currently configured to relay all mail out through SES using the code below. We need to modify this so that emails sent from one of our domains (domain.com) DO NOT go through SES. Everything else should continue to flow out through the SES connection. I'm assuming this is like a one line thing but my google skills are not helping me at all.

relayhost = email-smtp.us-east-1.amazonaws.com:25
smtp_sasl_auth_enable = yes
smtp_sasl_security_options = noanonymous
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_use_tls = yes
smtp_tls_security_level = encrypt
smtp_tls_note_starttls_offer = yes
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
smtp_destination_concurrency_limit = 450

Update I have created sender_transport file in /etc/postfix. In it is @domain.com smtp: I then ran this through postmap and placed sender_dependent_default_transport_maps = hash:/etc/postfix/sender_transport above the above block of code and restarted postfix, but still all email is going out through SES.

Log after sending

Oct 22 14:38:48 web postfix/smtp[19446]: 4B19D640002: to=<[email protected]>, relay=email-smtp.us-east-1.amazonaws.com[54.243.47.187]:25, delay=1.4, delays=0.01/0/0.92/0.44, dsn=2.0.0, status=sent (250 Ok 00000141e21b181f-ee6f7c4f-f0f5-4b0f-ba69-2db146a4f988-000000)
Oct 22 14:38:48 web postfix/qmgr[19435]: 4B19D640002: removed

I don't think this log is what you're looking for, but it's the only thing that is logged when mail goes out, and this is with me running /usr/sbin/postfix -v start manually and not with the init script.