Hello,
There are two things which you can check:
1) Default port for pop3 is 110 and for imap it is 143, so check if these two ports are open or not?
2) Check the URL which you are using in ur sender channel
a) For pop3 URL should be like: pop://host/
and
b) For imap it should be: imap://host/path/MyInBox
Thanks
Amit Srivastava