For myself, personally, I’ve never seen the value of digests. They make it hard to read only those messages which are actually interesting (based on subject line) and they’re murder to try and reply to without making a complete dog’s breakfast of the whole operation (everyone who’s seen a new thread on a mailing list with the subject
Re: <foo> digest, 1997-01-02 knows what I mean).
That being said, digest subscriptions have always made up a perplexingly large proportion of subscribers on any non-trivial mailing list I’ve had admin on, so if Discourse wants to have a really solid “mailman replacement” story, they are, sadly, something that’s going to have to be implemented.
As I understand it, the main blocker to daily digests is performance – busy topics/categories create many posts, which equals large e-mails, and huge strings, and performance sadness. The way that mailing list software has dealt with this since time immemorial is to have a size limit. You’re going to get at least one digest e-mail a day (if there are any new posts, anyway), but you may get more if things heat up. You can see this in, for example, the mailman digest configuration; specifically, the
One thing that makes it a lot easier for mailman, et al, to send out digests without exploding is that they can assemble a single digest for all subscribers and send it out rapid-fire, rather than having to hand-craft a new message for every subscriber based on each person’s individual tastes and circumstances. If it would be a worthwhile performance improvement, I think a similar strategy would work for Discourse: if you subscribe to digests for a category, you get all that category’s messages: no filtering, muting, etc, and if you subscribe to multiple categories, you get a separate digest e-mail per category, possibly on a different schedule to the e-mails for other categories. It’s how existing digest die-hards are used to things happening, so while I won’t be surprised if they complain (because a certain percentage of people will, just on principle), it’s easier to explain that this is how it worked before, and your cheese is just a teeny, tiny bit further to the left than it was, see, it’s right there, you can stop hyperventilating now please.