Knowledge Base

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

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)

Manual 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

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:
  
  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:
  
  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 perm…