What is this tool?

IMAP Authorization tool checks user credentials against given IMAP server. IMAP Authorization tool displays each command and response received from IMAP server. DNSStuff strongly recommends that you do not use a real email account when testing password authentication

Some of the popular pop servers IPs are –
98.137.151.55 (pop.mail.yahoo.com)
173.194.77.109 (pop.gmail.com)
65.55.206.154 (pop3.live.com)