Nginx won’t start at boot

The tutorial is from May 9th, 2010.
v1.2.6 2009-10-05 The last dovecot version before that date
v2.0.rc1 2010-07-02 The next dovecot version after that date

So the tutorial probably will use a 1.x configuration, while nowadays we will use dovecot 2.x. Well and A LOT has changed in how the configuration is set since then.

Now I found this http://wiki2.dovecot.org/Upgrading/2.0
Next to some other info, it provides a way to convert the config from 1.2 to 2.0.

Here's even more about upgrading http://wiki2.dovecot.org/Upgrading

I have no solution though (yet)

Edit:

Better solution
Just forget that tuorial from http://library.linode.com and use this up to date much better tutorial
http://www.exratione.com/2012/05/a-mailserver-on-ubuntu-1204-postfix-dovecot-mysql/
It also shows you how to install spam filter, anti virus detection and add more security to your mail server. Also with this solution you'll be able to very easily add multiple domains.
I had the solution below working first, now I switched to that solution and it works and does what I want perfectly.

Question related solution
But if you must exactly find a solution for the dovecot problem like described in the question, here's how I solved the problem...
also install:

apt-get install dovecot-sieve  
apt-get install dovecot-managesieved  
apt-get install dovecot-mysql  

if you like, read the hints on upgrading the old 1.x config http://wiki2.dovecot.org/Upgrading

My dovecot.conf:

log_timestamp = "%Y-%m-%d %H:%M:%S "
mail_location = maildir:/home/vmail/%d/%n/Maildir
namespace {
  inbox = yes
  location = 
  prefix = INBOX.
  separator = .
  type = private
}
passdb {
  args = /etc/dovecot/dovecot-sql.conf.ext
  driver = sql
}
protocols = imap pop3
service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0660
    user = postfix
  }
  unix_listener auth-master {
    mode = 0600
    user = vmail
  }
  user = root
}
ssl_cert = </etc/ssl/certs/dovecot.pem
ssl_key = </etc/ssl/private/dovecot.pem
#userdb {
#  args = uid=5000 gid=5000 home=/home/vmail/%d/%n allow_all_users=yes
#  driver = static
#}
userdb {
  args = /etc/dovecot/dovecot-sql.conf.ext
  driver = sql
}
protocol lda {
  auth_socket_path = /var/run/dovecot/auth-master
  log_path = /home/vmail/dovecot-deliver.log
  mail_plugins = sieve
  postmaster_address = postmaster@example.com
  plugin {
    sieve_global_path = /var/vmail/globalsieverc
    # The include extension fetches the :personal scripts from this 
    # directory. When ManageSieve is used, this is also where scripts 
    # are uploaded.

    sieve_dir = ~/sieve

    # The location of the user's active script:

    sieve = ~/.dovecot.sieve

    # Directory for :global include scripts (for v1.1 include extension)

    sieve_global_dir = /var/vmail/sieve

    sieve_maxscriptsize = 128
  }
}
protocol pop3 {
  pop3_uidl_format = %08Xu%08Xv
}

My dovecot-db.conf.ext

driver = mysql
connect = host=127.0.0.1 dbname=mail user=mail_admin password=your_password
default_pass_scheme = CRYPT
#password_query = SELECT email as user, password FROM users WHERE email='%u';
#user_query = SELECT email as user, password, 5000 as uid, 5000 as gid, '/var/vmail/%d/%n' as home FROM view_users WHERE email='%u';
password_query = SELECT email AS user, password, 5000 AS userdb_uid, 5000 AS userdb_gid, '/var/vmail/%d/%n' AS userdb_home FROM users WHERE email = '%u';
user_query = SELECT email AS user, password, 5000 AS uid, 5000 AS gid, '/var/vmail/%d/%n' AS home FROM users WHERE email = '%u';

My /etc/postfix/sasl/smtpd.conf (note the auxprop_plugin:sql, sql_engine:mysql, and the '%u@%r')

pwcheck_method: saslauthd
mech_list: plain login pam
allow_plaintext: true
auxprop_plugin: sql
sql_engine: mysql
sql_hostnames: 127.0.0.1
sql_user: mail_admin
sql_passwd: your_password
sql_database: mail
sql_select: select password from users where email = '%u@%r'

Sources:
I've gathered all infos about this by googling, and don't know where I was everywhere, but the last problem

2013-01-03 16:43:27 lda: Error: userdb lookup(info@example.com): Disconnected unexpectedly
2013-01-03 16:43:27 lda: Fatal: Internal error occurred. Refer to server log for more information.

I solved reading some of http://workaround.org/ispmail/lenny/configure-dovecot
Basically, I found that you get good results when you google whatever error output you get in here:

/home/vmail/dovecot-deliver.log
/var/log/mail.log
/var/log/mail.err
/var/log/syslog

could not access PID file for VPN 'server' means the PID file could not be read. This can have different reasons:

• you do not have the rights to read the pid file -- did you run the command as root or with sudo?
• the pid file does not exist, as the process is not running or could not create the file for some reason

Thus, for further debugging, you will need to look at /var/run/openvpn.server.pid itself

• does it exist?
• is there an openvpn process running with the pid listed in the file?
• are there other openvpn processes running?

If the process is not running, your config is most probably wrong and you will have to read the logs why it did not start. Running service openvpn start might bring helpful output too.