If DMARC is enabled in SpamTitan Gateway, the behavior of SPF could change. If you have SPF Reject enabled, mail that fails SPF during the initial SMTP handshake will still be rejected during the initial SMTP handshake, but only if the sending domain does not have a DMARC record.

If the sending domain does have a DMARC record, then the message body will be accepted and the policy that has been defined in the DMARC record will be applied. A DMARC policy can specify ‘none’, ‘quarantine’, or ‘reject’, see DMARC Policies below.

It is good practice to set up your DMARC record with a policy of ‘none’ initially to monitor where mail is being sent from. When you are confident that your SPF record is correct, then change the policy to 'quarantine' or 'reject'.