Helo All,

We had installed Post-fix mail service on Ubuntu 12.0.4 server. Configure dovecot also.
For this activity i refer Ubuntu's share document.

1) I am able to telnet SMTP protocol.
2) But POP3 not telnet.
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ganesh@ubuntu:~$ telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 mail.example.com ESMTP Postfix (Ubuntu)
bye
502 5.5.2 Error: command not recognized
quit
221 2.0.0 Bye
Connection closed by foreign host.
ganesh@ubuntu:~$ telnet localhot 110
telnet: could not resolve localhot/110: Name or service not known
ganesh@ubuntu:~$ sudo /etc/init.d/dovecot restart
[sudo] password for ganesh:
Rather than invoking init scripts through /etc/init.d, use the service(8)
utility, e.g. service dovecot restart

Since the script you are attempting to invoke has been converted to an
Upstart job, you may also use the stop(8) and then start(8) utilities,
e.g. stop dovecot ; start dovecot. The restart(8) utility is also available.
dovecot start/running, process 1457
ganesh@ubuntu:~$ telnet locahost 110
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Please suggest what i can do further. I will do my level the best. Thanks team for you support and guideline.

Can you post the output of telnet localhost 110.Because you have tried with localhot instead of localhost.

Did you see the typo??? You typed in "localhot", not localhost.
...and did you READ and UNDERSTAND the message the system gave you?? You ran it as /etc/init.d/dovecot restart, when it specifically tells you NOT TO, and tells you you might have to perform other steps to get that to work. Did you bother to try "service dovecot restart", as it told you?? "service dovecot stop" and then "start"????

You also don't say what guide you followed, or if you have any firewalls/selinux/iptables running.

ganesh@ubuntu:/$ telnet localhost 110
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection refused
ganesh@ubuntu:/$ sudo dovecot restart
doveconf: Warning: NOTE: You can get a new clean config file with: doveconf -n > dovecot-new.conf
doveconf: Warning: Obsolete setting in /etc/dovecot/dovecot.conf:21: 'imaps' protocol is no longer necessary, remove it
doveconf: Warning: Obsolete setting in /etc/dovecot/dovecot.conf:21: 'pop3s' protocol is no longer necessary, remove it
doveconf: Fatal: Error in configuration file /etc/dovecot/dovecot.conf line 93: Unknown setting: mechanisms
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I used ubuntus serverguide.pdf

Ok, you still haven't run "service dovecot restart" as it was suggested to you, or stopped/started things manually. And did you not read/understand the fatal error message that you got??? It's very plainly telling you there's an error in your dovecot.conf file, and even tells you what LINE it's on. Doesn't get much more plain than that. Did you LOOK at that line? Try to FIX that error????
...which STILL tells us nothing. You don't say where you got it, or provide a link, so we have NO IDEA what you've followed.

/
ganesh@ubuntu:/$ telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 mail.example.com ESMTP Postfix (Ubuntu)
quit
221 2.0.0 Bye
Connection closed by foreign host.
ganesh@ubuntu:/$ telnet localhost ^C
ganesh@ubuntu:/$ telnet localhost 110
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection refused
ganesh@ubuntu:/$ sudo service dovecot restart
[sudo] password for ganesh:
stop: Unknown instance:
dovecot start/running, process 1646
ganesh@ubuntu:/$ telnet localhost 110
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection refused
ganesh@ubuntu:/$
----------------------------------------------------------------------------
https://help.ubuntu.com/lts/serverguide/serverguide.pdf

AGAIN...did you look at line 93? The part YOU POSTED in the log file, that specifically TELLS YOU that you have a fatal error?? Did you look at that line? Fix it?

Posting the same results without actually addressing the errors the system gave you is pointless.