PostfixExamples

Example Config Files for Postfix Email Relay

These are a sanatized set of files that will allow SMTP relay functionality to M365 tenants. This is a semi-secure configuration (i.e. non-open relay). Additionally this relay was designed to be behind a firewall and no publicly accessible for inbound traffic.

Requirements

• Ability to create receive connector in M365
• Ability to send SMTP (Port 25) traffic outbound throught premise firewall
• Basic Linux Familiarity

Prerequisites

• Linux Server with Postfix installed
• Port 25 open on linux server

Contents

• main.cf
• local_domains
• open_access
• recipient_access
• restrict_senders
• transport

File Functions

main.cf = primary configuration file for postfix, most changes are at the bottom of this config file but a few settings are inline you need to pay attention for.

local_domains = these are your email domains

open_access = list of ip based devices that can use the relay

restrict_senders = list of from addresses that can use the relay

transport = configuration that points to M365

recipient_access = not sure what this does as I did not use it

Post configuration requirements.

After modifying the configuration files (all except "main.cf") you need to convert them to a db file. This is achieved by the postmap command. Example: postmap transport or postmap open_access, etc

Then you need to restart the postfix server for those changes to take effect. postfix stop, then postfix reload, then postfix start

Helpful Postfix Commands

postfix reload = reload postfix

postfix stop = stop postfix

postfix start = start postfix

postfix status = see status of postfix

postmap filename = update file map after changes to file

mailq = view mail queue

postqueue -p = print/view mail queue

postqueue -f = flush/release mail queue

tail -f /var/log/maillog | grep -B 2 -A 2 "emailaddress" = search log for messages