If you experience problems setting up your email client, or issues when sending emails, check which port is configured. In a typical scenario, when your SMTP server is configured to use SSL – or more precisely TLS – the default port is set as 465.
According to many sources, port 465 should not be used for SMTP with TLS connection, when sending emails. The default port should be 587.
Unfortunately, the latest cPanel/WHM 62.x, 64.x are still suggesting to use port 465 for TLS SMTP to send outgoing email, which creates a variety of problems.
If you are in doubt, just use port 25, which by default accepts TLS connections for outgoing email.
Port 587
This is the default mail submission port. When a mail client or server is submitting an email to be routed by a proper mail server, it should always use this port.
Port 465
IANA has reassigned a new service to this port, and it should no longer be used for SMTP communications.