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Ensuring email deliverability on Pantheon

Number of views : 30
Article Number : KB0015689
Published on : 2024-03-25
Last modified : 2024-03-25 14:34:24
Knowledge Base : IT Public Self Help


From Pantheon's Platform Considerations:

"Because of the cloud-based nature of Pantheon's infrastructure, we cannot ensure high-deliverability email originating from your Application Containers, as they have no fixed location. While all sites have access to a local Postfix service for testing and development, we recommend using an external SMTP gateway (SendGrid, for example) in production to ensure that your email is delivered".

The best way to set this up is using authenticated SMTP via the campus authenticated mail relay server (, using the appropriate Wordpress/Drupal plugin to send the application's mail to this external server.

Step 1: Request a Service EID

Follow the request form instructions at

You will need to provide:

  • A department code
  • Service name
  • EIDs of two technical contacts

In your request, indicate that this Service EID will be used for authenticating to the campus mail relay server.


Step 2: Whitelist Service EID

Send an email to with the following text, replacing "<EID>" with the actual Service EID username:


Please grant service EID, <EID>, rights to use  This is for <SITE_URL>, which is a website hosted on Pantheon.



Step 3: Configure website to use external SMTP gateway.

Drupal Configuration

Pantheon recommends using the SMTP Authentication Support Module.  After enabling the module, enter the following as a new "provider" at /admin/config/system/smtp 


Backup server N/A
Username Service EID
Password Service EID password
SMTP Port 25
Use encrypted Yes (TLS only, no SSL)


WordPress Configuration

Pantheon recommends using the WP Mail SMTP plugin.  After activating the plugin, set the following values in Settings -> WP Mail SMTP and save.


Mailer Other SMTP
SMTP Port 25 
Encryption TLS
Authentication On
SMTP Username Service EID
SMTP Password Service EID password


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