I was notified by a user that she was not able to check her email. After verifying that I could successfully establish a Telnet connection to the Simple Mail Transfer Protocol (SMTP) port, i.e., well-known port 25, which her system would use for sending email, I then tried establishing a Post Office Protocol version 3 (POP3) connection to the mail server from an external Microsoft Windows system, using Microsoft's telnet client. But that got stuck at "connecting to".
Microsoft Telnet> open mail.example.com 110 Connecting To mail.example.com...
So I logged into the mail server, which is a
CentOS 7 Linux server running
Sendmail
and
Dovecot, and tried connecting to the
localhost
address, 127.0.0.1, but Dovecot never responded with a banner, nor did I receive
any response when I issued a user command to provide login
credentials. I had to hit Ctrl-] to exit from the Telnet
program, since I wasn't getting any response from Dovecot.
# telnet 127.0.0.1 110 Trying 127.0.0.1... Connected to 127.0.0.1. Escape character is '^]'. user lila ^] telnet> quit Connection closed. #
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