VirtualMTA directive
smtp-source-host
Bind an outbound source IP and announce the matching HELO hostname.
PowerMTAv4.1 frameworkProduction reference
Production caution: Use an IP configured on the server. PTR and forward DNS should resolve consistently with the announced hostname.
Purpose
Bind an outbound source IP and announce the matching HELO hostname. This reference focuses on operational intent, placement, validation, and failure modes rather than presenting a value as universally safe.
Example syntax
smtp-source-host 192.0.2.10 mail1.example.comPlacement and scope
The effective scope depends on where the directive is placed: global, source, SMTP user, virtual MTA, pool, or destination domain. Keep related controls together and comment the business purpose of each override.
Verification procedure
- Back up the active configuration and included files.
- Confirm the directive is supported by the installed PowerMTA release.
- Validate every referenced VMTA, pool, file, hostname, IP address, selector, and pattern list.
- Reload safely and watch the main log for parser or runtime errors.
- Send a controlled test and inspect the exact source IP, EHLO, headers, TLS state, and SMTP response.
Common failure modes
- Placing the directive in a scope where it is ignored or overridden.
- Referencing an object that is misspelled or not defined.
- Copying syntax from a different PowerMTA version.
- Using aggressive values without measuring provider acceptance and queue age.