When apps like Ulysses and 1Password went down the subscription route, I had no issue with it because Ulysses has continued to get better and better over time (by adding great new features), and I use 1Password's cloud sync service (and I think there's an argument to be made that password management apps need to continue evolving with the web to maintain usability).<p>I realize Spark is doing a bit more than your run-of-the-mill email client, but I see that as an implementation detail / architectural decision more than I see that as a feature as an end user.<p>The email client space is mostly commoditizated, and the feature set is mostly standardized. I think that's why putting some of these features behind a subscription tier feels so gross to me.<p>Syncing my contacts to some cloud service and doing something special with them? Sure, charge me for that. Running my emails through some special spam service? (not that this is necessary if you use a decent provider), sure, charge for that.<p>Mute Thread and Group by Sender cost $4.99/month? No thank you.<p>I've been a Spark user for a long time, but I have no intention of paying for "Group by Sender", thank you very much.