Unable to receive or send e-mails in Plesk hosted on AWS/LightSail or Microsoft Azure: port 25 is blocked

Symptoms

• Unable to receive/send e-mails from Plesk hosted on Amazon Lightsail/AWS EC2 or Microsoft Azure instance

• The following error can be found in /var/log/maillog when sending emails to an external domain:

  CONFIG_TEXT: dsn=4.4.1, status=deferred (connect to alt2.gmail-smtp-in.l.google.com[142.250.4.26]:25: Connection timed out)

• The following error can be found in %plesk_dir%Mail Servers\Mail Enable\Logging:

  CONFIG_TEXT: Communications Error: Socket connection to gmail-smtp-in.l.google.com failed (error 10060). The host was either not contactable or it rejected your connection. Socket Family = 2; Host=203.0.113.2; Port=25

• Email notifications from Advanced Monitoring not delivering.

• Outgoing mail connections via 25 port are not possible:

  # telnet mail.example2.com 25
  Trying 203.0.113.2...
  telnet: connect to address 203.0.113.2: Connection timed out
  Trying 2001:db8:f61:a1ff:0:0:0:80... telnet: connect to address 2001:db8:f61:a1ff:0:0:0:80 Network is unreachable.

• It is possible to send out an email message locally using the command:

  # telnet localhost 25

• Notifications are received in regards to this port:

  CONFIG_TEXT: You cannot send emails from Plesk because outbound connections on TCP port 25 is blocked. Check the firewall settings or contact your hosting provider.

Cause

SMTP ports are blocked by a firewall from Amazon side or on the server.

Resolution

• For AWS instance, submit a request to AWS support to have port 25 unblocked in accordance with Amazon documentation or setup mail relay as shown in our free Udemy course.

  Warning: If you have Amazon Lightsale please explicitly mention in the link above that you need to remove the port block for LightSale, otherwise AWS team will remove it for EC2 only.

• For Microsoft Azure, contact support at Subscription Management Problem type: Request to enable Port 25 email flow.

• If the Plesk Firewall is used, open mail port under Plesk > Tools & Settings > Firewall;

• If the system or a third party firewall is active on the server, make sure that it is not blocking the connection to the 25,465,995 ports.

• In case of an intermediate firewall, it is required to contact the service provider.

Additional information

Unable to send emails using Plesk local mail server: Connection timed out or connection refused. (#4.4.1)
Which Ports Need To Be Opened for all Plesk Services to Work with a Firewall?