SMTP port 25 is closed (not listening) on a Windows Server with MailEnable mail server. It is not possible to telnet to this port:
C:> telnet localhost 25
Connecting To localhost…Could not open connection to the host, on port 25: Connect faile
Emails are not delivered from external mail services (Gmail, Outlook) to a Plesk mail server without any errors in MailEnable logfiles.
Custom SMTP port is specified in SMTP settings of MailEnable Management console.
Connect to a Plesk server via RDP.
Start MailEnable Management console at Windows Start > All Programs > MailEnable.
In MailEnable Management console, expand Servers > localhost > Services and Connectors > right-click on SMTP and open its Properties.
In SMTP properties window, switch to the Inbound tab > click Settings in the Port Settings section > set the setting SMTP service listens on port to 25. Apply the changes on both windows.
In MailEnable Management console, expand System > Services Status > click on MailEnable SMTP Connector > Restart on the right pane.