Sendmail to Relay Emails through Gmail STMP

This tutorial will help you to configure Sendmail to relay email through external smtp servers like Gmail, Amazon SES, Mailchimp, Mandrill etc. In this tutorial we are suing Gmail SMTP server to relay emails from sendmail server.

1. Create Auth File

First create directory for storing authentication files.

$ sudo mkdir /etc/mail/auth
$ sudo chmod 700 /etc/mail/auth

Now create a auth file with any name like smtp-auth and add following content. Replace the above email with your gmail or google apps email.

$ sudo vi /etc/mail/auth/smtp-auth

AuthInfo: "U:root" "I:[email protected]" "P:PASSWORD"

Now create a hash map file of above created auth file.

$ makemap hash /etc/mail/auth/smtp-auth < /etc/mail/auth/smtp-auth

2. Configure Sendmail with SMART_HOST

Now add following configuration lines into your sendmail.mc configuration file below "MAILER" definition.

define(`SMART_HOST',`[smtp.gmail.com]')dnl
define(`RELAY_MAILER_ARGS', `TCP $h 587')dnl
define(`ESMTP_MAILER_ARGS', `TCP $h 587')dnl
define(`confAUTH_OPTIONS', `A p')dnl
TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
FEATURE(`authinfo',`hash -o /etc/mail/authinfo/smtp-auth.db')dnl

In the next step we will need to re-build sendmail's configuration. To do that execute:

# make -C /etc/mail

3. Verify Setup

After completing all above configuration, reload sendmail service.

$ sudo service sendmail reload

Now send a test email verify everything is working fine.

$ echo "Test Email" | mail -s "Subject Here" [email protected]