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Custom SMTP vs. default SMTP

Knowledge Drop

Last tested: Jul 1, 2019

By default, all Looker mail will go through our 3rd party SMTP service  -- Sendgrid.

When a schedule is ready to send content to an email destination after the query has finished running, it will be passed on to the mailer. The mailer bundles the content in an email with headers, a link back to Looker, and then sends it on to the SMTP service.

With default SMTP, the email will go to Sendgrid which will then send it on to the email address the content was intended for.

With a custom SMTP setup, the email will be sent to the email server that is configured in the Admin panel. That SMTP server can do whatever filtering, blocking or transforming it likes before sending the mail on to the final destination.

Description of Fields:

Mail Server

This needs to be only the domain name (e.g. without the scheme (https://) and also without any path. Even a trailing slash will be considered a path (e.g. will not work)


This will be the name of the sender that the recipient of the email sees when they receive the email. This field is optional, but recommended.


Username is almost always a full email address. The Password needs to be re-entered if making any changes to any of the fields. Caution: Chrome will sometimes autofill the username and password when you load the SMTP admin page, overwriting the current settings.


This can be anything, as it depends on the configuration of the SMTP email server. That said, most servers use the following conventions:

  • 25 -- This is the original, default SMTP port specified the IETF. It's still commonly used, though many organizations block or filter this port due to security concerns, in favor of TLS/SSL SMTP authentication.
    • GCP-hosted customers will no longer be able to use port 25 because GCP blocks outbound port 25 globally (documentation).
  • 465 -- SSL (usually)
  • 587 -- TLS (usually)
  • 2525 -- Sometimes used as a mirror for 587 (TLS)


TLS and SSL are "cryptographic protocols", which means that they are industry-standard methods of allowing computers to encrypt their communications with other computers. This configuration in the custom SMTP settings will depend on the configuration of the SMTP server being used, however, most SMTP servers should be using TLSv1.2 since TLSv1.1 is starting to become considered deprecated by many tech companies, such as Google.

Check out the docs for more information on setting up and testing Custom SMTP in Looker.

NOTE for GSuite: Go inside the GSuite account and select "Enable Less Secure Apps"

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Version history
Last update:
‎06-14-2021 06:15 PM
Updated by: