Hi,
When using an external SMTP server, Invision sends the domain name of the SMTP SERVER in the HELO/EHLO commands, instead of the CLIENT (i.e. the server Invision is running on).
This is incorrect and violates the SMTP standard (RFC 2821), which says:
This information -- the domain name of the server Invision is running on -- is readily available, for example, from the license key URL.
Here's the incorrect code in Smtp.php, with HELO/EHLO being sent with the SMTP server's name ($this->smtpHost)
This is causing mail servers to reject outbound mail (error 550).
Please fix this asap. Happy to provide more logs/information if needed.