How to configure Postfix SMTP relay office365 on Centos

 

Postfix:

Postfix is a flexible mail server that is available on most Linux distribution. Though a full featured mail server, Postfix can also be used as a simple relay host to another mail server, or smart host. This tutorial will describe how to configure Postfix as a relay through Office365.

 

Requirement:

CentOS  or Red Hat Enterprise Linux 
Valid Office365 email credentials.

Installation:

Install Postfix using command below

[root@localhost ~]# yum install postfix cyrus-sasl-plain mailx

 

Configuration changes:

Postfix main configuration file is main.cf, let's make the required change as follow:

[root@localhost ~]# vi /etc/postfix/main.cf

 Append the following line

relayhost = [smtp.office365.com]:587

mynetworks = 127.0.0.0/8

inet_interfaces = loopback-only

smtp_use_tls = yes

smtp_always_send_ehlo = yes

smtp_sasl_auth_enable = yes

smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd

smtp_sasl_security_options = noanonymous

smtp_sasl_tls_security_options = noanonymous

smtp_tls_security_level = encrypt

smtp_generic_maps = hash:/etc/postfix/generic

#smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt

sender_canonical_classes = envelope_sender, header_sender

sender_canonical_maps =  regexp:/etc/postfix/sender_canonical_maps

smtp_header_checks = regexp:/etc/postfix/header_check




Rewrite envelope address from email originating from the server itself

/etc/postfix/sender_canonical_maps:

/.+/    newsender@address.com

Rewrite from address in SMTP relayed e-mail

/etc/postfix/header_check:

/From:.*/ REPLACE From: newsender@address.com

 

Save and exit from the file.

The configuration of postfix SASL credentials:

[root@localhost ~]# vi /etc/postfix/sasl_passwd

Add a line below

[smtp.office365.com]:587 user@domainname:password

Save and exit from file

 

A Postfix lookup table must now be generated from the sasl_passwd text file by running the following command.

[root@localhost ~]# postmap /etc/postfix/sasl_passwd

Now change permission for this file

[root@localhost ~]# chown root:postfix /etc/postfix/sasl_passwd

[root@localhost ~]# chmod 640 /etc/postfix/sasl_passwd

 

 

Next let's correct the file permission.

[root@localhost ~]# chown root:root /etc/postfix/generic

[root@localhost ~]# chmod 0600 /etc/postfix/generic

[root@localhost ~]# postmap /etc/postfix/generic

 

/etc/postfix/main.cf:

 

Let's restart Postfix service.

[root@localhost ~]# systemctl restart postfix

 

Now try to send a test email using the command below:
FOR  Centos:

echo "This is the body of the email"| mail -r"Sender-Display-Name<sender@domain.com>" -s "This is the subject(E-Mail from SMTP Relay) line" recipeat@gmail.com