Yes, you have to check with any mail client that the POP3 credentials you are trying to use (username and password) are working fine. We are talking here about the legacy POP3 authentication and not any modern one like OAuth.
If you validate the POP3 credentials with any mail client and using them in Axigen still create problems we’ll have to use a simple openssl POP3 login test session to double check those credentials.
HTH,
Ioan