Resolution
If you are having connection problems with your SMTP server, perform the following steps to find the reason:- Make sure that you are using the right IP address and port number combination for the SMTP server in your mail client preferences. If you are using the domain name instead of the mail server IP, make sure that the domain is resolved to the right IP (see article 765).
- Check if Plesk SMTP service is running on the server (see article 1378).
- If SMTP service is working on the server, but you still cannot connect to it to send mail, the most likely reason is a firewall. Stop any firewall running on the Plesk server and try to send mail again. If this doesn't work, then the SMTP port is blocked from somewhere in your network. Please check your network and ask your ISP about port 25 filtering.