How to configure Postfix on a Plesk server to send emails using SendGrid

kb: how-to Plesk for Linux ABT: Group B

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Plesk for Linux

Question

How to configure Postfix to send emails using SendGrid in Plesk?

Answer

Starting with Plesk Obsidian 18.0.64, Smarthost can be configured via Plesk interface. Configuring a smarthost is a server-wide feature. For this feature to be implemented on per domain basis please vote for the following UserVoice.

Warning: The configuration below is not compatible with the Plesk Email Security extension. Consider removing it before applying the changes below.

Smarthost (preferred solution)

1. Choose a reputable SMTP relay service (for example, SendGrid, Mailgun, Mailjet, or any other) and create an account there.

2. Log in to Plesk

3. Go to Tools & Settings > Smarthost (under “Mail”).

4. Select the “Send users’ mail via a smarthost” checkbox.

5. In the corresponding field, specify the IP address or hostname of a smarthost (for example, 192.0.2.1 or smtp.sendgrid.net).

For more detailed steps please refer to the following documentation page:

Configuring a Smarthost or Relayhost

Manual Solution

Connect to the server via SSH.
Define which MTA is installed on the server and switch to Postfix if necessary.
Create a backup of the original /etc/postfix/main.cf configuration file and open it with a text editor:

# cp -a /etc/postfix/main.cf{,.original}
# vi /etc/postfix/main.cf
Modify the following:
- Add the SendGrid SMTP service as relayhost to the /etc/postfix/main.cf configuration file:
  
  CONFIG_TEXT: relayhost = [smtp.sendgrid.net]:2525
  
  Note: That port 2525 is used because the outbound connections on ports 25, 587 are not allowed on Google Compute Engine.
- Add the following lines at the end of the file:
  
  CONFIG_TEXT: smtp_tls_security_level = encrypt
  smtp_sasl_auth_enable = yes
  smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
  header_size_limit = 4096000
  smtp_sasl_security_options = noanonymous
  smtp_sasl_tls_security_options = noanonymous
Additional step for Google Cloud instances

Check if the following parameters exist and if so, comment them out by adding a hashtag sign in the beginning of the line:

default_transport = error
relay_transport = error

Commented out directives

#default_transport = error
#relay_transport = error

After the parameters are set, make sure that there are no duplicate directives that can break the configuration:

# cat /etc/postfix/main.cf | grep -E "relayhost|smtp_sasl_auth_enable|smtp_sasl_password_maps|smtp_sasl_security_options|smtp_sasl_tls_security_options|smtp_tls_security_level|header_size_limit"

Comment out/remove duplicate directives if there are some.
Generate the SASL password map using the API key from the SendGrid panel:

Note: Replace <your_SendGrid_API_Key_value> in the command below with the real API Key value:

# echo [smtp.sendgrid.net]:2525 apikey:<your_SendGrid_API_Key_value> >> /etc/postfix/sasl_passwd
Use the postmap utility to generate a .db file:

# postmap /etc/postfix/sasl_passwd
Verify that the .db file has been created:

# ls -l /etc/postfix/sasl_passwd*
-rw------- 1 root root ... /etc/postfix/sasl_passwd
-rw------- 1 root root ... /etc/postfix/sasl_passwd.db
Set proper permissions on the .db file:

# chmod 600 /etc/postfix/sasl_passwd.db
Remove the file containing SendGrid API Key as it is no longer needed:

# rm /etc/postfix/sasl_passwd
Reload Postfix service to apply changes:

# service postfix restart

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