A The port numbers of Mail Servers generally refers to the following table below.

POP server+SSL OFF	110
POPserver+SSL ON	995
IMAPserver+SSL OFF	143
IMAP server+SSL ON	993
SMTP server+SSL OFF	25or 587
SMTP server+SSL ON	465or 587

Most of the mail servers generally uses the port numbers above, however
there are some exceptional mail server.
Please look up the website of your mail service or contact to the administrator.