Unable to send emails to certain recipients in Plesk : 25: Connection timed out

• Unable to send email from the server to certain recipients.

• The following can be found in /var/log/maillog:

  main postfix/smtp[16855]: connect to mx.example.com:25: Connection timed out
  main postfix/smtp[16855]: BE46D121BD6: [email protected], relay=none, delay=150, delays=0.13/0.01/150/0, dsn=4.4.1, status=deferred (connect to mx.example.com:25: Connection timed out)

• Outgoing mail mode is set to Send from the specified IP addresses and IPv4 is set to 203.0.113.2 in Tools & Settings > Mail Server Settings.

• Emails are successfully sent if Send from domain IP addresses is enabled in Tools & Settings > Mail Server Settings or if QMail is selected in Tools & Settings > Mail Server Settings > Installed mail server.

• In Tools & Settings > IP Addresses there is a private IP address 192.0.2.2, for which a public IP address 203.0.113.2 is assigned and there is a separate IP address 203.0.113.2.

Cause

Non-routable IP address 203.0.113.2 is being used for sending emails.

Resolution

1. Log into Plesk

2. Go to Tools & Settings > Mail Server Settings and switch Outgoing mail mode to internal IP address 192.0.2.2 or another IP address that is routable on this server.