Error message "Unable to change format for subscription because email attachments are disabled. Contact your Tableau administrator for details."

Issue

Error "Unable to change the format and download the email subscriptions on Tableau Server" when trying to change the format of attachments on an existing subscription in Tableau Server. Also the dropdown UI to set a format type will be missing when setting up a new subscription on a view.

Environment

Tableau Server 2019.3.x and later
Windows Server

Resolution

There are two settings that if not enabled would produce this error message;

1. Enable the setting "Let users add attachments to subscribed views." on the TSM server settings as per step 3 https://help.tableau.com/current/server/en-us/email.htm
2. Enable the setting "Let users add attachments to subscribed workbooks and views." on each server site as required as per 3a https://help.tableau.com/current/server/en-us/subscribe.htm

Even if the setting is enabled at the TSM level, the same error message will display if the required setting is not enabled at a site level also.