How To: Restricting IMAP/POP3 access

Below examples show how you can give POP3 access to everyone, but IMAP access only for some people. The exact solution you want depends on what passdb you use. The solutions can also be modified for other types of IMAP/POP3/SMTP/etc. access checks.

PAM

Set PAM service name to %s, ie.:

passdb {
  driver = pam
  args = %s
}

That way PAM uses /etc/pam.d/imap for IMAP, and /etc/pam.d/pop3 for POP3.

In /etc/pam.d/imap you could then use, e.g., the pam_listfile.so module:

# allow IMAP access only for users in /etc/imapusers file
auth    required        pam_listfile.so item=user sense=allow file=/etc/imapusers onerr=fail

SQL

You can use the %s variable which expands to imap or pop3 in password_query:

password_query = SELECT password FROM users WHERE userid = '%u' \
    and not (imap_allowed = false and '%s' = 'imap')

LDAP

Just like with SQL, you can use %s in pass_filter:

pass_filter = (&(objectClass=posixAccount)(uid=%u)(service=%s))

That would require setting both service=pop3 and service=imap attributes to the user objects.

passwd-file

You can create a deny passwd-file based on the service:

passdb {
  driver = passwd-file
  args = /etc/dovecot/deny.%s
  deny = yes
}

This makes Dovecot look for /etc/dovecot/deny.imap and /etc/dovecot/deny.pop3 files. If the user exists in it, the access is denied. The files don't need to have anything else than one username per line.

Note that this deny passdb must be before other passdbs. It also means that it can be used with any other passdb, not just with passwd-file passdbs.

Restricting IP Access

It's possible to allow a user to authenticate only from a specific IP or network. This is especially useful for master users. This can be done by returning allow_nets extra field from passdb extra fields.