I did install Email with Postfix, Dovecot and MySQL on Ubuntu 10.04 LTS (Lucid)
http://library.linode.com/email/postfix/dovecot-mysql-ubuntu-10.04-lucid#sph_more-information

Last entries:
chgrp vmail /etc/dovecot/dovecot.conf
chmod g+r /etc/dovecot/dovecot.conf

Then the POP3 server failed:
telnet localhost pop3

Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection refused

How can I solve the issue?
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These entries/warnings may help to identify the problem and how can I fix these?

/var/log/mail.log
Sep 12 15:40:21 xxxx dovecot: master: Dovecot v2.0.19 starting up (xxxx dumps disabled)
Sep 12 15:40:21 xxxx dovecot: ssl-params: Generating SSL parameters
Sep 12 15:40:27 xxxx postfix/master[6876]: daemon started -- version 2.9.3, configurati$
Sep 12 15:40:37 xxxx dovecot: ssl-params: SSL parameters regeneration completed
Sep 13 08:41:23 xxxx postfix/master[2296]: daemon started -- version 2.9.3, configurati$
Sep 13 08:41:33 xxxx dovecot: master: Dovecot v2.0.19 starting up (xxxx dumps disabled)
Sep 13 10:10:19 xxxx postfix/master[2296]: terminating on signal 15
Sep 13 10:10:19 xxxx postfix/master[3190]: daemon started -- version 2.9.3, configurati$
Sep 13 11:36:44 xxxx dovecot: log: Warning: Killed with signal 15 (by pid=1 uid=0 code=$
Sep 13 11:36:44 xxxx dovecot: master: Warning: Killed with signal 15 (by pid=1 uid=0 co$

service postfix restart - generates warnings i.e.:
* Starting Postfix Mail Transport Agent postfix postconf: warning: /etc/postfix/main.cf: unused parameter: virtual_create_maildirsize=ye s
postconf: warning: /etc/postfix/main.cf: unused parameter: virtual_maildir_extended=yes
postconf: warning: /etc/postfix/main.cf: unused parameter: virtual_create_maildirsize=ye s
...
/usr/sbin/postconf: warning: /etc/postfix/main.cf: unused parameter: virtual_create_mail dirsize=yes
/usr/sbin/postconf: warning: /etc/postfix/main.cf: unused parameter: virtual_maildir_ext ended=yes
...

If you run cat /etc/*release I think you'll find that you're using Ubuntu 12.04, not 10.04. Differences between the releases mean you can't follow the Library article verbatim.

I will restore my backup to the point of the LAMP server installation. Can you recommend a stack that installs everything at ones needed for a complete mail server?

I installed the mail server new and tried now the setup: https://mail.example.com/postfixadmin/setup.php

I receive this error: Secure Connection Failed
Error code: ssl_error_rx_record_too_long

I checked: Listen 443 https, look OK.

What can trigger this problem or did I miss something?