First, make sure TELNET is installed on your machine else you’ll get error. You can install TELNET through Add or Remove feature on Windows.
You can use TELNET via a command prompt to confirm.

For IMAP check port 143 and if using SSL then check port 993.

For POP3 check port 110 and if using SSL then check port 995.

Test POP3 connection:

• Start a command prompt
• Enter TELNET {webserver} port e.g. TELNET exchangesrvr01 995
• Enter USER {login} e.g. USER testemail@mycomp.com
• Enter PASS {password} e.g. PASS secret
• Enter LIST to show the mailbox
• Enter QUIT to Exit

At each stage you should receive an OK message. If there is an issue at any stage you will receive an error

Test IMAP connection:

• Start a command prompt
• Enter TELNET {webserver} port e.g. TELNET exchangesrvr01 143
• Enter . LOGIN {login} {password} e.g. LOGIN testemail@mycomp.com secret
• Enter . LIST “” “*” to show the mailbox
• Press CTRL + ] and then QUIT to Exit

At each stage you should receive an OK message. If there is an issue at any stage you will receive an error.