Sending email with Mailgun

Mailgun is a third-party email service that offers Compute Engine users up to 10,000 free email messages each month. Mailgun also offers a programmatic API, log retention, email personalization, analytics, email validation, and more.

Follow these instructions to sign up for and use Mailgun.

Before you begin

  1. Create a new Mailgun account on Mailgun's Google partner page*. As a Compute Engine user, your first 30,000 messages are free every month. Check out the Mailgun monthly pricing calculator for pricing on additional messages and volume discounts.

  2. Get your credentials. The instructions require that you know your Mailgun SMTP username, password, and hostname. Get your username and password from the Mailgun control panel, under the Domains section.

    The Mailgun SMTP hostname is

  3. Configure your firewall rules to allow outgoing traffic on TCP port 2525.

* Google is compensated for customers who sign up for a non-free account.

Configuring Mailgun as a mail relay with Postfix

Configuring Mailgun as a mail relay allows the Postfix mail transfer agent to forward emails destined for remote delivery.

  1. Connect to your instance using SSH.

    gcloud compute ssh [INSTANCE_NAME]

    where [INSTANCE_NAME] is the name of the VM instance where you want to send email from.

  2. Become a superuser and set a safe umask.

    user@test-instance:~$ sudo su -
    root@test-instance:~# umask 077
  3. Install the Postfix Mail Transport Agent. When prompted, accept the default choices for domain names but select the Local Only configuration.


    root@test-instance:~# apt update && apt -y install postfix libsasl2-modules


    root@test-instance:~# yum install postfix cyrus-sasl-plain cyrus-sasl-md5 -y

  4. Modify the Postfix configuration options. Postfix configuration options are set in the file. Open the file with the text editor of your choice.

    root@test-instance:~# vi /etc/postfix/
  5. If they exist, comment out the following lines.

    # default_transport = error
    # relay_transport = error
  6. Add the Mailgun SMTP service by adding the following line to the end of the file.

    relayhost = []:2525
  7. Next, add the following lines to enforce SSL/TLS support and to configure STMP authentication for these requests. A simple access and security layer (SASL) module handles authentication in the Postfix configuration. Add the following lines to the end of the file.

    smtp_tls_security_level = encrypt
    smtp_sasl_auth_enable = yes
    smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
    smtp_sasl_security_options = noanonymous

    Save your changes and close the file.

  8. Generate the SASL password map.

    1. Create a new password file that is ready for standard input.

      root@test-instance:~# cat > /etc/postfix/sasl_passwd << EOF
    2. At the prompt, enter the service details, replacing YOUR_SMTP_LOGIN and YOUR_SMTP_PASSWORD with your credentials. See the Mailgun help for instructions on how to view or change your per-domain credentials.

    3. Close and save the file by typing the delimiter, EOF.

      > EOF
  9. Use the postmap utility to generate a .db file.

    root@test-instance:~# postmap /etc/postfix/sasl_passwd
    root@test-instance:~# ls -l /etc/postfix/sasl_passwd*
    -rw------- 1 root root    68 Jun  1 10:50 /etc/postfix/sasl_passwd
    -rw------- 1 root root 12288 Jun  1 10:51 /etc/postfix/sasl_passwd.db
  10. Next, remove the file that contains your credentials because it is no longer needed.

    root@test-instance:~# rm /etc/postfix/sasl_passwd
  11. Set the permissions on your .db file.

    root@test-instance:~# chmod 600 /etc/postfix/sasl_passwd.db
    root@test-instance:~# ls -la /etc/postfix/sasl_passwd.db
    -rw------- 1 root root 12288 Aug 31 18:51 /etc/postfix/sasl_passwd.db
  12. Finally, reload your configuration to load the modified parameters.


    root@test-wheezy:~# /etc/init.d/postfix restart


    [root@test-centos ~]# postfix reload

  13. Test your configuration. Install the mailx or mailutils package and test your configuration.


    root@test-wheezy:~# apt -y install mailutils


    [root@test-centos ~]# yum install mailx -y

    Send a test message.

    root@test-instance:~# echo 'Test passed.' | mail -s 'Test-Email' EMAIL@EXAMPLE.COM

    Look in your systems logs for a status line containing status and the successful server response code (250).


    root@test-wheezy:~# tail -n 5 /var/log/syslog


    [root@test-centos ~]# tail -n 5 /var/log/maillog

For detailed examples and information about other topics including tracking and routing messages, read the Mailgun documentation.

Mailgun SMTP settings

Use the following Mailgun-specific SMTP settings to configure clients:

  • Host:
  • Port: 2525

Try out other Google Cloud features for yourself. Have a look at our tutorials.