Dovecot

root@mail:~# aptitude install dovecot-common dovecot-core dovecot-sieve dovecot-ldap dovecot-imapd dovecot-managesieved

Configuração padrão:

root@mail:~# doveconf -n
# 2.2.13: /etc/dovecot/dovecot.conf
# OS: Linux 3.16.0-4-amd64 x86_64 Debian 8.0 
mail_location = mbox:~/mail:INBOX=/var/mail/%u
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date ihave
namespace inbox {
  inbox = yes
  location = 
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  prefix = 
}
passdb {
  driver = pam
}
plugin {
  sieve = ~/.dovecot.sieve
  sieve_dir = ~/sieve
}
protocols = " imap sieve"
ssl = no
userdb {
  driver = passwd
}

Usuário para administrar as caixas postais

root@mail:~# groupadd -g 240 vmail
root@mail:~# useradd -m -g 240 -u 240 -d /home/vmail -s /bin/false vmail