Dovecot and Postfix Hybrid Authentication Example

This guide assumes you already have postfix installed, dovecot installed, and at minimum have email established for unix accounts either by final destination or virtual alias domains. Now you want to set up a separate virtual user database, and these virtual users that do not have a unix account on the system will be able to retrieve their email from their virtual mailbox. The security benefit is in that email only users need not have any security credentials in the /etc/passwd and still be able to pop or imap in and retrieve email.

It might make things more clear to first Understand Postfix Account Types for a Linux system.

Locate your postfix configuration files, they might be in /etc/postfix, or /etc/mail/postfix, or /etc/mail depending on your distro and installation.

This document is not complete... here is a summary

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• Set up postfix virtual mailbox text file with email address and destination folder - this is plain text file that must be made hash database
• Make sure all domains are configured in postfix
• create a passwd file for each virtual user domain /etc/passwd.domain.com
• edit dovecot/conf.d/auth-checkpassword.conf.ext

mail_location = maildir:~/Maildir
passdb {
 driver = pam
}
 driver = passwd-file
 args = /etc/postfix/passwd/%d

Here are (some) important lines you will need in your main.cf

alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
home_mailbox = Maildir/
virtual_alias_maps = hash:/etc/postfix/virtual
virtual_mailbox_domains = hash:/etc/postfix/domains
virtual_mailbox_base = /var/spool/vmail
virtual_mailbox_maps = hash:/etc/postfix/vmailbox
virtual_minimum_uid = 4000
virtual_uid_maps = static:5000
virtual_gid_maps = static:5000

Here is a sample of (minimum) lines from dovecot.conf

protocols = imap pop3 lmtp
listen = *
login_greeting = Hello visitor!
!include conf.d/*.conf

The 10-auth.conf is located in the conf.d/ folder. Here is a sample of (minimum) lines from 10-auth.conf

disable_plaintext_auth = no
auth_failure_delay = 4 secs
auth_mechanisms = plain login
!include auth-system.conf.ext
!include auth-checkpassword.conf.ext

Make sure that !include auth-checkpassword.conf.ext is uncommented.

The auth-checkpassword.conf.ext is in the conf.d/ filder. Here are all the necessary lines.

passdb {
  driver = passwd-file
  args = /etc/postfix/passwd/%d
}

userdb {
  driver = prefetch
}

userdb {
  driver = passwd-file
  args = /etc/postfix/passwd/%d
}

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