Testing email protocols by typing out command over a network protocol

Summary

• You can test email protocols by typing out the commands over a network connection.
  For example, for POP3 you can !!!!TELNET!!!! on port 110

• We cant test POP3S over telnet because you can't just type out the SSL handshake.
  You can use openssl s_client to replace telnet when connecting to a POP3S server. s_client does the SSH handshake and allows you to type data over the encrypted connection like telnet allows over unencrypted.

Testing POP3 on port 110:

Type the following command on terminal:

$ telnet [host] [port]

eg: telnet 192.168.123.4 110

Then after +OK The Microsoft Exchange POP3 service is ready.
Type USER followed by the username then hit enter
Then type PASS followed by the password

eg:

USER test@your-domain 

Then enter:

PASS testing

Then a message will be displayed to specify whether the correct credentials were provided or not.

Testing POP3 on port 995:

Type the following command on terminal.

$ openssl s_client -connect [host]:[port] -crlf

eg: openssl s_client -connect 192.168.123.4:995 -crlf

Then after +OK The Microsoft Exchange POP3 service is ready.
Type USER followed by the username then hit enter
Then type PASS followed by the password

eg:

USER test@your-domain 

Then enter:

PASS testing

Then a message will be displayed to specify whether the correct credentials were provided or not.