Configuring a Server-Wide Smarthost

You can configure a smarthost for the whole server. This works in Plesk for Linux with Postfix and Plesk for Windows with either MailEnable or SmarterMail.

To configure a server-wide smarthost:

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

2. Войдите в 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).

   Примечание

   In Plesk for Linux, you can disable MX or SRV lookups by putting the hostname or IP address in square brackets, for example, [example.com]. For details, see the Postfix documentation (the section about relayhost).

6. If your SMTP relay service requires SMTP authentication (and most services do), select the «Authentication required» checkbox.

7. If you have selected «Authentication required» during the previous step, specify the credentials to authenticate to your SMTP relay service.

   If the service supports basic authentication, specify the username and password in the corresponding fields. If the service supports authentication via API keys, in the «Username» field, specify the default username used for API keys in the service (for example, in SendGrid, the username is apikey) and, in the «Password» field, specify the API key value.

8. (For SmarterMail only) In the «Encrypted connection» section, select whether to encrypt the credentials transmitted to the SMTP relay service. Choose if the encrypted connection is TLS, SSL, or not required.

   Примечание

   If you choose a connection type that the SMTP relay service does not support (for example, SSL instead of TLS), the smarthost will refuse the connection.

9. (Optional) You may want to check if the connection to the smarthost can be established. To do so, click Check Connection.

   If you selected “Encrypted connection” in the previous step, Plesk tests the connection not only for encryption but also for a valid SSL/TLS certificate. If the connection is encrypted but the SSL/TLS certificate is not trusted (for example, expired or self‑signed), the smarthost will refuse the connection.

   Примечание

   You can change the default behaviour described above and allow to establish the connection even if it is not secured by a valid SSL/TLS certificate.

10. Нажмите OK.

11. Update the SPF and other related DNS records in the DNS template and in the DNS zones of existing domains. SMTP relay services provide the information what DNS changes to make.

    You have configured the smarthost on the Plesk side. However, most commercial SMTP relay services require domain authentication on their side (can also be called domain verification). The following SMTP relay services require it: SendGrid, Mailjet, Mailgun.

12. Go to your SMTP relay service account and authenticate all domains hosted in Plesk. For exact steps on how to do so, refer to the documentation of your service.

13. Send a test email to an external email service (for example, Gmail) and make sure that the email has reached the inbox.

You have configured the smarthost both in Plesk and your SMTP relay service. Your smarthost is now up and running.

Configuring Smarthost for a Domain

You can configure a smarthost for an individual domain. This works in Plesk for Linux with Postfix and Plesk for Windows with either MailEnable or SmarterMail.

To configure a smarthost for a domain:

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

2. Войдите в Plesk.

3. Go to Websites & Domains > [domain_name] > Mail > Smarthost.

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).

   Примечание

   In Plesk for Linux, you can disable MX or SRV lookups by putting the hostname or IP address in square brackets, for example, [example.com]. For details, see the Postfix documentation (the section about relayhost).

6. If your SMTP relay service requires SMTP authentication (and most services do), select the «Authentication required» checkbox.

7. If you have selected «Authentication required» during the previous step, specify the credentials to authenticate to your SMTP relay service.

   If the service supports basic authentication, specify the username and password in the corresponding fields. If the service supports authentication via API keys, in the «Username» field, specify the default username used for API keys in the service (for example, in SendGrid, the username is apikey) and, in the «Password» field, specify the API key value.

8. (Optional) You may want to check if the connection to the smarthost can be established. To do so, click Check Connection.

9. Нажмите OK.

10. Update the SPF record in the DNS zone of the domain you configured. This ensures the SMTP relay service is authorized to send mail for this domain.

    You have configured the smarthost on the Plesk side. However, most commercial SMTP relay services require domain authentication on their side (can also be called domain verification). The following SMTP relay services require it: SendGrid, Mailjet, Mailgun.

11. Go to your SMTP relay service account and authenticate the domain you just configured smarhost for in Plesk. For exact steps on how to do so, refer to the documentation of your service.

12. Send a test email to an external email service (for example, Gmail) and make sure that the email has reached the inbox.

You have configured the smarthost both in Plesk and your SMTP relay service. Your smarthost is now up and running.

If you want to check which domains have an active smarthost, go to Mail> Smarthosts.

Configuring a Smarthost After a Previous Manual Configuration

If you have already configured a smarthost manually, enabling the smarthost feature in Plesk will overwrite your existing configuration. Although Plesk applies the most common configuration suited for most smarthost services, you may need to tinker with the configuration to tailor it to your smarthost.

If you have already configured a smarthost manually, we recommend you the following algorythm:

1. Compare both smarthost configurations: your manual one and the one from Plesk.

2. Remove the parameters that will be controlled by Plesk from your manual configuration.

3. Keep additional parameters not covered by Plesk as it is.

4. Enable the smarthost feature in Plesk.

To help you compare both configurations, below we describe how the smarthost feature works under the hood: which configuration files it affects and in what way.

(Plesk for Linux) Smarthost Configuration with Postfix

When you enable the smarthost feature, Plesk performs a few actions under the hood.

For server-wide smarthost:

1. Plesk adds lines of the following pattern to the /etc/postfix/main.cf configuration file:

   # Sets an external SMTP relayhost with a port number
   relayhost - [Your-SMTP-server-IP-or-hostname]:587
   # Turns on authentication
   smtp_sasl_auth_enable = yes
   # Sets the username and password required for authentication
   smtp_sasl_password_maps = /var/spool/postfix/plesk/relay_secrets
   # Prohibits anonymous authentication methods.
   smtp_sasl_security_options = noanonymous
   

2. Plesk then checks that /etc/postfix/main.cf contains no duplicate directives, which can break the configuration:

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

3. Plesk configures the API authentication to the SMTP relay service of your choice via the /etc/postfix/sasl_passwd file. For example, with the SendGrid service, the following line will be added:

   [smtp.sendgrid.net]:2525 apikey:<your-SendGrid-API-key-value>
   

4. Finally, Plesk reloads the Postfix service to apply the changes:

   systemctl reload postfix
   

For a domain-specific smarthost:

1. If no server-wide smarthost has been previously configured, Plesk adds the required baseline Postfix directives to the /etc/postfix/main.cf configuration file and also adds per-domain routing and credentials (no global relayhost is needed):

   # Turns on authentication
   smtp_sasl_auth_enable = yes
   # Sets the username and password required for authentication
   smtp_sasl_password_maps = hash:/var/spool/postfix/plesk/relay_secrets.db
   # Prohibits anonymous authentication methods.
   smtp_sasl_security_options = noanonymous
   # Enables per‑sender authentication and routing
   smtp_sender_dependent_authentication = yes
   # Maps sender addresses to specific relay hosts
   sender_dependent_relayhost_maps = hash:/var/spool/postfix/plesk/sender_relay.db
   

2. Plesk then checks that /etc/postfix/main.cf contains no duplicate directives, which can break the configuration:

   cat /etc/postfix/main.cf | grep -E "smtp_sasl_auth_enable|smtp_sasl_password_maps|smtp_sasl_security_options|smtp_sender_dependent_authentication|sender_dependent_relayhost_maps"
   

3. Plesck adds or updates the sender‑dependent mapping files used for domain‑level smarthosts

   • /var/spool/postfix/plesk/sender_relay.db — maps domains to their relay hosts.

   • /var/spool/postfix/plesk/relay_secrets.db — stores credentials for the corresponding relay hosts.

   For example, with the SendGrid service, Plesk writes entries similar to:

   # sender_relay
   admin@example.com    [smtp.sendgrid.net]:587
   
   # relay_secrets
   [smtp.sendgrid.net]:587    apikey:<your-SendGrid-API-key-value>
   

4. Finally, Plesk reloads the Postfix service to apply the changes:

   systemctl reload postfix
   

(Plesk for Windows) Smarthost Configuration with MailEnable

When you enable the smarthost feature, Plesk applies the MailEnable configuration shown on the screenshot below. We use the SendGrid SMTP relay service as an example.

The first screenshot shows the server-wide configuration, while the second one—the configuration for domains.

(Plesk for Windows) Smarthost Configuration with SmarterMail

When you enable the smarthost feature, Plesk applies the SmarterMail configuration shown on the screenshots below. We use the SendGrid SMTP relay service as an example.

The first screenshot shows the server-wide configuration, while the second one—the configuration for domains.

Disabling the Smarthost Feature

You may want to disable the smarthost feature by hiding it in the Plesk graphical interface.

To disable the smarthost feature:

1. Откройте для редактирования файл panel.ini, который находится здесь:

   • (Plesk для Linux) /usr/local/psa/admin/conf/panel.ini

   • (Plesk для Windows) %plesk_dir%admin\conf\panel.ini

   Вы также можете редактировать файл в интерфейсе Plesk, используя расширение Panel.ini Editor.

2. To disable smarthost at the server level, add the following lines to the panel.ini file, and then save it:

   [mail]
   smarthost.server.enabled = false
   

The smarthost feature is no longer shown in Tools & Settings.

1. To disable smarthost at the domain level, add the following lines to the panel.ini file, and then save it:

   [mail]
   smarthost.domain.enabled = false
   

The smarthost feature is no longer shown in Websites & Domains > [domain_name] > Mail.

Disable the SSL/TLS Certificate Check Bound With the Check Connection Button

By default, if the connection to a smarthost requires encryption, clicking Check Connection also verifies whether the connection uses a valid SSL/TLS certificate. If the certificate is invalid or missing, the smarthost will refuse the connection.

If you want to establish the connection even if an SSL/TLS certificate is not trusted (for example, expired or self-signed), you can disable the check of the certificate.

To disable the check of an SSL/TLS certificate bound with the Check Connection button:

1. Откройте для редактирования файл panel.ini, который находится здесь:

   • (Plesk для Linux) /usr/local/psa/admin/conf/panel.ini

   • (Plesk для Windows) %plesk_dir%admin\conf\panel.ini

   Вы также можете редактировать файл в интерфейсе Plesk, используя расширение Panel.ini Editor.

2. For disabling the check of the certificate at server level, add the following lines to the panel.ini file, and then save it:

   [mail]
   smarthost.server.checkConnection.checkCertificate = false
   

3. For disabling the check of the certificate at domain level, add the following lines to the panel.ini file, and then save it:

   [mail]
   smarthost.domain.checkConnection.checkCertificate = false
   

You can now establish the connection with a smarthost which is not secured with a valid SSL/TLS certificate.