Effective on 1 September 2017, our SMTP server will reject any outgoing message that uses a sender address in the form of “user@host.webfaction.com” (for example, “bob@web555.webfaction.com”).

This change primarily affects customers who are using sendmail (including the PHP mail() function) to send messages without explicitly setting a sender address.

If you’re not sure if you will be affected by this change, then send yourself a message from the potentially-affected website, script, or other application, and then inspect the headers of the received message to ensure that the “From” header is a valid address not in the form of “user@host.webfaction.com”, and does not use any of the domains listed in our email limitations and restrictions.

If you have any questions or concerns regarring this change, please open a support ticket and our team will be happy to assist.

2017-09-01 17:09 UTC: The new restrictions are now in effect.

2017-09-17 18:24 UTC: This change was disrupting outgoing email for several customers’ WordPress sites, so we’ve rolled it back and will re-deploy when that issue has been resolved.