Postfix SMTP authentication using dovecot

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Postfix SMTP authentication can work using both dovecot and cyrus. To use dovecot for SMTP authentication use following steps:

1. In /etc/dovecot/conf.d/10-master.conf as part of "service auth" there should be a unix_listener at /var/spool/postfix/private/auth using following configuration:

   service auth {
   unix_listener auth-userdb {
   }
   
   # Postfix smtp-auth
   unix_listener /var/spool/postfix/private/auth {
   mode = 0660
   user = postfix
   group = postfix
   }
   }

2. In /etc/dovecot/conf.d/10-auth.conf set auth_mechanisms to both plain and login using:

   auth_mechanisms = plain login

3. service dovecot restart
4. Configure postfix to use socket created by dovecot for authentication using following lines appended in /etc/postfix/main.cf file:

   #Indicates use dovecot auth
   smtpd_sasl_type = dovecot
   
   #Specified location of authentication socket supplied by dovecot
   #wrt /var/spool/postfix
   smtpd_sasl_path = private/auth
   
   #Enable SASL authentication
   smtpd_sasl_auth_enable = yes
   
   #Also advertize "AUTH PLAIN=" along with "AUTH PLAIN " to support broken clients esp outlook
   broken_sasl_auth_clients = yes
   
   #Do not allow anonymous access for SASL.  Very important
   #If SSL or TLS is configured then perhaps noplaintext over
   #non-encryption channel can also be configured
   smtpd_sasl_security_options = noanonymous
   #smtpd_sasl_security_options = noanonymous, noplaintext
   
   #Do not allow anonymous access for SASL over TLS/SSL.  Here
   #plaintext auth should not be a problem
   smtpd_sasl_tls_security_options = noanonymous
   
   #Allow relay for anybody sending to mydomain and allow relay from trusted networks.
   #Further allow relay to any destination from anywhere for authenticated clients
   smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
   
   #Append username of user who authentication in email headers
   smtpd_sasl_authenticated_header = yes

5. service postfix restart
6. Test authentication using
   1. telnet <mail-server> 25
   2. EHLO test
   3. AUTH PLAIN <auth-string>

      where auth-string can be obtained using "echo -ne '\000username\000password' | openssl base64" by replacing username and password appropriately

Steps learned from http://www.postfix.org/SASL_README.html#server_sasl_enable

Troubleshooting Relay access denied after successful authentication

If "Relay access is denied" even after successful authentication then try appending this to /etc/postfix/main.cf:

smtpd_recipient_restrictions =
    permit_sasl_authenticated
    permit_mynetworks
    reject_unauth_destination

and do "service postfix restart"

Steps learned from http://serverfault.com/questions/42519/how-to-correct-postfix-relay-access-denied

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