There are many reasons why you would want to configure Postfix to
send email using an external SMTP provider such as Google Apps (Gmail),
Mandrill, SendGrid, Amazon SES, or any other SMTP server. One reason is
to avoid getting your mail flagged as spam if your current server’s IP
has been added to a spam list.
In this tutorial, you will learn how to install and configure a
Postfix server to send email through Google Apps, Mandrill, or SendGrid.
Prerequisites
Before starting this tutorial, you should have:
- Debian 7 installed on your Linode
- Your fully qualified domain name (FQDN)
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All updates installed :
- A valid username and password for the SMTP mail provider, such as Google Apps, Mandrill, or SendGrid
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Make sure the libsasl2-modules package is installed and up to date:
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| sudo apt-get install libsasl2-modules
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This guide is written for a non-root user. Commands that require elevated privileges are prefixed with sudo. If you’re not familiar with the sudo command, you can check our Users and Groups guide.
Installing Postfix
In this section, you will install Postfix and set the domain and hostname.
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Install Postfix with the following command:
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| sudo apt-get install postfix
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During the installation, a prompt will appear asking for your General type of mail configuration.

Select Internet Site.
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Enter the fully qualified name of your domain, fqdn.example.com.

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Once the installation is finished, open the
/etc/postfix/main.cf file with your favorite text editor:
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| sudo nano /etc/postfix/main.cf
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Make sure that the myhostname parameter is configured with your server’s FQDN:
- /etc/postfix/main.cf
-
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| myhostname = fqdn.example.com
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Configuring SMTP Usernames and Passwords
Usernames and passwords are generally stored in a file called
sasl_passwd in the
/etc/postfix/ directory. In this section, you’ll add your external mail provider credentials to this file and to Postfix.
If you want to use
Google Apps,
Mandrill, or
SendGrid as your SMTP provider, you may want to reference the appropriate example while working on this section.
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Open or create the
/etc/postfix/sasl_passwd file, using your favorite text editor:
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| sudo nano /etc/postfix/sasl_passwd
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Add your destination (SMTP Host), username, and password in the following format:
- /etc/postfix/sasl_passwd
-
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| [mail.isp.example] username:password
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If you want to specify a non-default TCP Port (such as 587), then use the following format:
- /etc/postfix/sasl_passwd
-
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| [mail.isp.example]:587 username:password
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Create the hash db file for Postfix by running the
postmap command:
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| sudo postmap /etc/postfix/sasl_passwd
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If all went well, you should have a new file named
sasl_passwd.db in the
/etc/postfix/ directory.
Securing Your Password and Hash Database Files
The
/etc/postfix/sasl_passwd and the
/etc/postfix/sasl_passwd.db files created in the previous steps contain your SMTP credentials in plain text.
For security reasons, you should change their permissions so that only the
root
user can read or write to the file. Run the following commands to
change the ownership to root and update the permissions for the two
files:
1
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| sudo chown root:root /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db
sudo chmod 0600 /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db
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Configuring the Relay Server
In this section, you will configure the
/etc/postfix/main.cf file to use the external SMTP server.
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Open the
/etc/postfix/main.cf file with your favorite text editor:
1
| sudo nano /etc/postfix/main.cf
|
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Update the relayhost parameter to show your external SMTP relay host. Important: If you specified a non-default TCP port in the
sasl_passwd file, then you must use the same port when configuring the relayhost parameter.
- /etc/postfix/main.cf
-
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2
| # specify SMTP relay host
relayhost = [mail.isp.example]:587
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Check the appropriate Google Apps, Mandrill, or SendGrid section for the details to enter here.
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At the end of the file, add the following parameters to enable authentication:
- /etc/postfix/main.cf
-
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| # 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
# where to find CA certificates
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
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- Save your changes.
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Restart Postfix:
1
| sudo service postfix restart
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Testing Postfix
The fastest way to test your configuration is to send an email to any unrelated email address, using the
mail command:
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| echo "body of your email" | mail -s "This is a Subject" -a "From: you@example.com" recipient@elsewhere.com
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Alternatively, you can use Postfix’s own sendmail implementation, by entering lines similar to those shown below:
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| sendmail recipient@elsewhere.com
From: you@example.com
Subject: Test mail
This is a test email
.
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Examples of Postfix Configurations with Different Providers
This section shows you settings for some popular mail services you
can use as external SMTP servers. You may have to do some fine-tuning on
your own to avoid Postfix logins being flagged as suspicious.
Settings for Google Apps
Use these settings for Google Apps.
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For
/etc/postfix/sasl_passwd, use the following configuration with your own credentials:
- /etc/postfix/sasl_passwd
-
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| [smtp.gmail.com]:587 <USERNAME@gmail.com>:PASSWORD
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If you are using Google Apps with your own domain, configure /etc/postfix/sasl_passwd with:
- /etc/postfix/sasl_passwd
-
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| [smtp.gmail.com]:587 <USERNAME@yourdomain.com>:PASSWORD
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For
/etc/postfix/main.cf, use the following relayhost:
- /etc/postfix/main.cf
-
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| relayhost = [smtp.gmail.com]:587
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Create the hash db file for Postfix by running the
postmap command:
1
| sudo postmap /etc/postfix/sasl_passwd
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Restart Postfix:
1
| sudo service postfix restart
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Settings for Mandrill
Use these settings for Mandrill.
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For
/etc/postfix/sasl_passwd, use the following configuration with your own credentials:
- /etc/postfix/sasl_passwd
-
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| [smtp.mandrillapp.com]:587 USERNAME:API_KEY
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For
/etc/postfix/main.cf, use the following relayhost:
- /etc/postfix/main.cf
-
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| relayhost = [smtp.mandrillapp.com]:587
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Create the hash db file for Postfix by running the
postmap command:
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| sudo postmap /etc/postfix/sasl_passwd
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Restart Postfix:
1
| sudo service postfix restart
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Settings for SendGrid
Use these settings for SendGrid.
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For
/etc/postfix/sasl_passwd, use the following configuration with your own credentials:
- /etc/postfix/sasl_passwd
-
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| [smtp.sendgrid.net]:587 USERNAME:PASSWORD
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For
/etc/postfix/main.cf, use the following relayhost:
- /etc/postfix/main.cf
-
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| relayhost = [smtp.sendgrid.net]:587
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Create the hash db file for Postfix by running the
postmap command:
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| sudo postmap /etc/postfix/sasl_passwd
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Restart Postfix:
1
| sudo service postfix restart
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