You can manually interact with a POP server to perhaps manually delete an email that your mail too is having trouble downloading, or simply to check things out. Here's a sample manual session:
$ telnet pop.ktware.com 110 Trying 184.108.40.206... Connected to pop.ktware.com. Escape character is '^]'. +OK Hello there. USER kayon +OK Password required. PASS Secret +OK logged in. LIST +OK POP3 clients that break here, they violate STD53. 1 2269 2 1498 3 2816 4 2113 . RETR 1 +OK 2269 octets follow. Return-Path: <[email protected]> Delivered-To: [email protected] ... . DELE 1 +OK Deleted. QUIT +OK Bye-bye. Connection closed by foreign host.