Problem

How to setup a Mail Relay for a subscription in a Plesk Control Panel?
How to setup outMail for a number of subscriptions on a Plesk Control Panel?
How to setup a SMTP Mail Relay on a Plesk Control Panel?

Solution

Follow the guide below to configure a domain/subsciption to sending emails using outMail as a Internet Mail Relay instead of the default SMTP gateway already setup on the Plesk.

This article already assumes your Plesk system is able to send emails externally and that you are already have a terminal/shell connection to your server with the necessary access rights to manage and administor postfix.

In this example we will assume you have a subscription setup on the Plesk with a domain called example.com and instead of emails going the default way you want emails from example.com to go via outMail SMTP Email relay service.  It is further assumed you have already signed up for a outMail service and you have the assigned outMail server and SMTP credentials.

Step 1 - Gather your outMail Credentials

You will need your outMail credentials in order to configure postfix in the Plesk.  ou can find those details in the Portal as well as your original welcome email.

Example of credenitals

Step 2 - Create DNS CNAME records

Assuming that you will want multiple outMail accounts to assigned to multiple subscription respectively you will also need to create DNS CNAME for each assigned outMail server.

Example of CNAMES

Step 3 - Create a postfix relay file

[example-com-outmail.mydomain.com]:25 example-username:example-password

where example-username and example-password are the (case-sensitive) information provided when you set up your account.

The format of the /etc/postfix/relay_passwd file is as follows

[CNAME_HOSTNAME]:OUTMAILPORT OUTMAILUSERNAME:OUTMAILPASSWORD

Step 4 - Create a postfix relay map file

Now we need to create a postfix map file for postfix to use. Create a file called /etc/postfix/relay_map and add the following lines to that file

@example.com [example-com-outmail.mydomain.com]:25

where [example-com-outmail.mydomain.com]:25 must match what you entered in the relay_passwd file and must be the same as the CNAME created.

The format of the /etc/postfix/relay_map file is as follows

@example.com [CNAME_HOSTNAME]:OUTMAILPORT

Step 5 - postmap

We now need to create lookup databases from those two files using postmap.

postmap /etc/postfix/relay_map 
postmap /etc/postfix/relay_passwd 

Step 6 - Make changes to the posttix configuration

To enable postfix to use the outMail service for those domains we type the following.

postconf -e smtp_sasl_auth_enable=yes
postconf -e sender_dependent_relayhost_maps=hash:/etc/postfix/relay_map 
postconf -e smtp_sasl_password_maps=hash:/etc/postfix/relay_passwd 
postconf -e smtp_sasl_security_options=noanonymous
postconf -e smtp_sasl_security_options=$smtp_sasl_security_options

Step 7 - restart postfix

For the above changes to take effect the postfix service will need restarting (service postfix restart).

service postfix restart

Adding a second domain

You now have a second domain (acme.com) from a different subscription that also wants to send out using outMail, but with different outMail credentials.  In addition you want to send to outMail using a different SMTP port (In this example 2525).

Example of credenitals

Step 1 - Add another CNAME

Create DNS CNAME for each of the assigned outMail services.

Note: Even if the assigned outMail server is the same as previous entries still create the additional CNAME.  Reason for this is the CNAME is used in the /etc/postfix/relay_map and /etc/postfix/relay_passwd files to link the subscription to the respective outMail service and credentials.

Updated CNAMES

Step 2 - Modify the postfix relay file

With shell/console access to the Plesk server you need to edit the existing password file (/etc/postfix/relay_passwd).

[example-com-outmail.mydomain.com]:25 example-username:example-password
[acme-com-outmail.mydomain.com]:2525 acme-username:acme-password

where acme-username and acme-password are the (case-sensitive) information provided when you set up your outMail service for acme.com.

Step 3 - Modify the postfix relay map file

Now we need to edit postfix map file (/etc/postfix/relay_map).

@example.com [example-com-outmail.mydomain.com]:25
@acme.com [acme-com-outmail.mydomain.com]:2525	

where [acme-com-outmail.mydomain.com]:2525 must match what you entered in the relay_passwd file.

Step 4 - postmap

We now need to re-create lookup databases from those two files using postmap.

postmap /etc/postfix/relay_map 
postmap /etc/postfix/relay_passwd 

Step 5 - restart postfix

For the above changes to take effect the postfix service will need restarting (service postfix restart).

service postfix restart

Additional Steps

Below are some additional steps you might want to consider.

SPF Support

As you domain is now sending out bound emails via outMail you should add to your existing SPF record the outMail SPF record.

More information on this can be found in this KB Article -> How to create a Sender Policy Framework (SPF) Record to Authorise outMail Servers to send out your Email

DKIM Support

outMail supports the DKIM of signing of emails.

If you want to DKIM sign emails then a useful guide can be found in this KB Article -> How do I enable DKIM signing of emails through outMail?

Problem Solving

Below is a list of common gotchas.

SASL authentication failure

In your postfix logs you see message smilar to "mail postfix/smtp: warning: SASL authentication failure"

Double check you did the following

postmap /etc/postfix/relay_passwd
postfix reload