I currently use IFTTT to send me an email for each new feed item from questions I am interested in on Stack Exchange but I would much rather use Stack Exchange's own filters feature with email updates.
The problem I have with it though is that I get all the questions from today bundled together in a single email thread/conversation. (See email subscribe to tag sets always uses the same subject line.)
This means that if I get several emails and I'm "done" with the questions from one email message I cannot mark it as done independently from all the other questions for today.
I would love to have a feature to instead of get an email update when new questions arrive in a filter every 15 minutes / 3 hours / day to get an email for each question as soon as feasible (every 15 minutes is fine but as the emails aren't bundled they can come as quickly as Stack Exchange is willing and able to send them).