Below is a guide on how to setup Postfix mail server on RHEL 7 to relay emails through Zoho Mail.
There are a number of reasons as to why you would want to use an external SMTP server to relay your emails. You can configure it with with your application to send email alerts. You can also use it to relay emails if you happen to have your IP address blacklisted.
Also, using an external SMTP provider is one way to ensure that your email isn’t flagged as spam. This however is not a loophole to send spam emails. The mail service providers have extensive measures put in place to ensure users don’t abuse the email service.
- A fully qualified domain name.
- A valid username and password for Zoho Mail.
Installing Postfix and Mailutils
yum install postfix mailutils
Create a file to store your account details and smtp server details.
Now we need to hash the postfix password and set proper permissions and set proper permissions on the original file.
The postmap command is used to hash the postfix password.
Since this file contains SMTP credentials in plain text, the permissions and ownership should be edited such that only the root user can read and write the file.
chown root:root /etc/postfix/sasl_passwd/etc/postfix/sasl_passwd.db
chmod 0600 /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db
Configuring the Relay Server
Open /etc/postfix/main.cf , which is the main configuration file, with your favorite text editor and add the following configurations.
# specify SMTP relay host relayhost = [smtp.zoho.com]:587 # enable SASL authentication smtp_sasl_auth_enable = yes # disallow methods that allow anonymous authentication. smtp_sasl_security_options = noanonymous # where to find sasl_passwd smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd # Enable STARTTLS encryption smtp_use_tls = yes smtp_tls_wrappermode = yes smtp_tls_security_level = encrypt # where to find CA certificates smtp_tls_CAfile = /etc/ssl/certs/ca-bundle.crt smtp_tls_session_cache_database = btree:/var/lib/postfix/smtp_tls_session_cache smtp_tls_session_cache_timeout = 3600s sender_canonical_classes = envelope_sender, header_sender sender_canonical_maps = regexp:/etc/postfix/sender_canonical smtp_header_checks = regexp:/etc/postfix/smtp_header_checks
/etc/postfix/sender_canonical and put in your Zoho email address:
/etc/postfix/smtp_header_checks and put in your Zoho email address
/From:.*/ REPLACE From: email@example.com
Save the changes once done, reload postfix and use the command below to send a test message.
service postfix restart
echo “test message” | mailx -s “test subject” firstname.lastname@example.org
In case of any issues, check out /var/log/maillog to troubleshoot