Unable to send email to Yahoo mailboxes from a Linux Plesk server: said: 550 5.7.25 Forward-confirmed reverse DNS failed tnmpmscs

Symptoms

• Unable to send email to Yahoo from mailbox hosted in Plesk, while receiving bounceback messages that are similar to the following:

  CONFIG_TEXT: 550 5.7.25 Forward-confirmed reverse DNS failed tnmpmscs (in reply to MAIL FROM command))

• The /var/log/maillog contains errors that are similar to the following:

  CONFIG_TEXT: Aug 18 09:12:56 server postfix/smtp[851082]: 248561C8C8B8: to=<example@yahoo.com>, relay=mx-eu.mail.am0.yahoodns.net[203.0.113.2]:25, delay=0.52, delays=0.02/0/0.45/0.05, dsn=5.7.25, status=bounced (host mx-eu.mail.am0.yahoodns.net[203.0.113.2] said: 550 5.7.25 Forward-confirmed reverse DNS failed tnmpmscs (in reply to MAIL FROM command))

• The server IP address 203.0.113.2 has a PTR record that resolves to a hostname, similarly to the following:

  # dig -x 203.0.113.2 + short
  mail.example.com

Cause

The mail.example.com hostname (which is present in the PTR record of your server IP address), resolves to an IP address that is not configured on the Plesk server.

Since the email itself does not originate from that IP address when you are sending it, this is viewed as a significant discrepancy by Yahoo, due to which they reject the email that you are sending.

The hostname that you have selected as a PTR record for your server's IP address must always resolve to the server's IP address and no other IP addresses.

Note: Having additional IP addresses associated to the A records for the same hostname can also lead to inconsistencies during reverse DNS validation and reputation checks performed by receiving mail providers.

Resolution

You have two general options to resolve such an issue: