I am using Jetpack, JP-Protect and WP-Mail-SMTP.
Recently, I started getting errors with WP-Mail-SMTP sending emails. The interesting thing is that, when I try to send a test mail from the dedicated WP-Mail-SMTP page, it works. It also works when I call wp_mail from my own code.
Otoh it seems to fail with Jetpack – WP-Mail-SMTP helpfully pinpoints the caller.
The error message from the SMTP server is:
data not accepted.SMTP server error: DATA END command failed Detail: Domain name ‘www.circularrevolution.org’ must be added, and validated, before using it
SMTP code: 551 Additional SMTP info: 5.5.3
The ‘www.circularrevolution.org’ is teh address of the website. The smpt server is set up to handle email for ‘circularrevolution.org’, with no www prefix