On February 28, 2018, Sitecore turned off the Email Preview and Spam Check services. The reason is that Litmus decided to deprecate their legacy API, which we used as a part of Sitecore Email Experience Manager (EXM) Email Preview and Spam Check services.
Litmus retired their API in 2018 because they had a new product offering. The new product did not allow an OEM integration, so it was not a viable part of our partnership. Customers can utilize the service but must sign up with Litmus directly.
This applies to all EXM and App Center versions.
The Email Preview and Spam Check functionality no longer appears in the user interface for Sitecore Email Experience Manager (EXM) releases compatible with Sitecore XP 9. For ECM/EXM releases compatible with Sitecore XP 8 or earlier, these features still appear but stopped working from 28 February 2018.
Customers can work directly with Litmus, but the solution will not be white labelled into the platform. They can use a seed list or a copy and paste approach to make this simpler but this is based on Litmus' own functionality.
For any further questions, customers are welcome to contact a Sitecore regional sales representative.