To ensure that the known subscriptions issues are not causing a problem I have included the following Online Help document:
Additionally, some users have problems when sending through encrypted SMTP servers, as Tableau Server does not support encrypting subscription views. Though unlikely, please ensure that the SMTP server does not use encryption and that TLS is deselected as shown in Tableau Server Configuration.
Replying to an old topic but I ran into the same issue. Hopefully this helps someone:
If you are seeing "Invalid Addresses" as the error in the Background Tasks for Non Extracts view try and check the backgrounder logs (..\data\tabsvc\logs\backgrounder).
Mine was being thrown by "SMTPAddressFailedException: 550 5.7.1 Unable to relay". The company I was working for had an exchange server that only had Internal SMTP Relay configured, and not External SMTP Relay. This means that my email address which was not part of the company was rejected and the Tableau subscription failed.