In certain circumstances, you may receive this error when trying to send outbound messages through our service:
This can happen for the following reasons:
To reduce risk of abuse, outbound email messages can only be sent "From" domains that are subscribed to the SpamHero service (domain aliases are included). There is an exception to this rule for messages that are sent to recipient domains that are subscribed to the SpamHero service (e.g. mail that doesn't leave our network).
Our Outbound SMTP service supports forwarding messages on behalf of external domains when any of the following conditions are met:
When forwarding mail, your server may need to be configured to adjust the Return-path of the original messages. This can be accomplished using the Sender Rewriting Scheme (SRS) feature on most mail servers.
The original purpose of SRS is to prevent forwarded emails from breaking SPF, however, it also allows forwarded emails to be relayed through our outbound service.