Google Cloud works with Mailgun to provide an email service that has a programmatic API, log retention, email personalization, analytics, and email validation.
The following instructions show you how to configure Mailgun as an email relay with Postfix.
Before you begin
Sign up for and create a new Mailgun account on the Google Cloud Marketplace.
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.
Depending on how the domain is configured in Mailgun, the SMTP hostname is either
smtp.mailgun.org
orsmtp.eu.mailgun.org
.Configure your firewall rules to allow outgoing traffic on TCP port
2525
.
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.
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.Become a superuser and set a safe umask.
user@test-instance:~$ sudo su -
root@test-instance:~# umask 077
Install the Postfix Mail Transport Agent.
Debian
root@test-instance:~# apt update && apt -y install postfix libsasl2-modules
CentOS
root@test-instance:~# yum install postfix cyrus-sasl-plain cyrus-sasl-md5 -y
When prompted, select the
Local Only
configuration and accept the default choices for domain names.Modify the Postfix configuration options. Postfix configuration options are set in the
main.cf
file. Open the file with the text editor of your choice.root@test-instance:~# vi /etc/postfix/main.cf
If they exist, comment out the following lines.
# default_transport = error # relay_transport = error
Add the Mailgun SMTP service by adding the following line to the end of the file.
relayhost = [smtp.mailgun.org]:2525
To enforce SSL/TLS support and configure SMTP authentication for these requests, add the following lines to the end of the file. A simple access and security layer (SASL) module handles authentication in the Postfix configuration.
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.
Generate the SASL password map.
Create a new password file that is ready for standard input.
root@test-instance:~# cat > /etc/postfix/sasl_passwd << EOF
At the prompt, enter the service details, replacing
YOUR_SMTP_LOGIN
andYOUR_SMTP_PASSWORD
with your credentials. See the Mailgun help for instructions on how to view or change your per-domain credentials.> [smtp.mailgun.org]:2525 YOUR_SMTP_LOGIN:YOUR_SMTP_PASSWORD
Close and save the file by typing the delimiter,
EOF
.> EOF
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
Next, remove the file that contains your credentials because it is no longer needed.
root@test-instance:~# rm /etc/postfix/sasl_passwd
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
Finally, reload your configuration to load the modified parameters.
Debian
root@test-wheezy:~# /etc/init.d/postfix restart
CentOS
[root@test-centos ~]# postfix reload
Test your configuration. Install the
mailx
ormailutils
package and test your configuration.Debian
root@test-wheezy:~# apt -y install mailutils
CentOS
[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)
.Debian
root@test-wheezy:~# tail -n 5 /var/log/syslog
CentOS
[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.
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