The outgoing filtering solution operates independently from the incoming email solution and is used to relay outgoing mail.
Requirements & Limitations
Relaying through the outbound filter has some requirements for mail to be accepted. In addition to the configuration of relay addresses and outbound authentication, the SMTP From addresses used to send mail from must be able to receive mail. If a sender address returns a failure to an inbound recipient callout, the outbound message/connection will be rejected.
Steps to Configure
Outgoing mail filtering includes several aspects that require attention:
- Create the Outgoing User - Create an outgoing authentication user to authenticate all outgoing mail against
- Configure the Abuse Report Address - Set up an abuse report address to be informed every time an outgoing senders message is rejected
- Set up SPF - Configure the Sender Policy Framework used to restrict which mail servers are allowed to send email for your domain name
- Set up DMARC - Set up the DMARC record on the DNS to choose the policy or action taken to messages that fail the DMARC check
- Set up DKIM - Set up a DKIM record to sign messages and help authenticate the senders as much as possible
- Outbound Filtering Hostnames - Configure your SMTP Hostname to use the correct ports and SPF records