I just installed a fresh vserver with Debian 11.8 and Version 18.0.56. I can receive emails but not send. I checked the port 25 is open. When I send email from webmail not error is displayed. Any idea?
By default Plesk on Linux uses Postfix for outgoing email, and by default listens on port 25 for outgoing SMTP mail. Some service providers do not allow to send emails on that port, and tragedy occ…
You have to contact your provider where you get the server from. Ask them if port 25 is open for outgoing traffic. Most providers won't open port 25 unless you ask them to.