Change: Restored the Digest feature
This version restores the Digest feature.
Firstly, I want to apologise for how this happened and how I handled this. I did not adequately communicate my plans to remove this feature, and as a result I did not give people a chance to voice their feedback. I arrogantly assumed that people used Digests in an entirely different way (as a way to bring back old, lapsed users), and I did not consider that people might have purchased Mail exclusively for this feature.
To everyone affected by this: I'm sorry. I will do better in the future.
Going forward, if I ever think a XenForo feature supersedes an add-on feature, I will post my plans to remove the feature as an update in the resource @ XenForo.com.
Secondly, I'd like to share the roadmap for the Digest feature going forward.
Beta 1: Restoration of the Digest feature as it was in v4.4
Beta 2: Replace the current "Content type" sections with a custom implementation of the Activity Summary sections
Beta 3: Address feedback with the new "Content type" sections
The reason for replacing the existing "Content type" section with an implementation of "Activity Summary" sections is that not only will it better support core XenForo / official add-ons, but other 3rd party add-ons will likely add support for the "Activity Summary" feature going forward. Being able to automatically support this in DB Mail would be a net benefit.
Unfortunately I cannot give an ETA for when Beta 2+ will be released, since it's going to be a significant amount of work.