I've switched to mu4e for email for a while. It's got a lot in common with notmuch. The motivation for switching is the UI for reading mail.
I find that the search capabilities of both notmuch and mu4e are good. The combination of tagging, probabilistic free text search, and email header awareness makes it much more effective than any of the traditional email clients that I have tried. I'm now a little bit spoiled by having the ability to do a free text search on all 25,000 emails in my archive in less than 100 milliseconds. (The contrast with the glacial often broken Lotus Notes that I must use for work is painful.) The one important difference is that tags are in the mail index for notmuch, while tags are in X-headers in the emails for mu4e. So mu4e must modify the email file to add or remove a tag.
My motivation for switching is that the email reader for notmuch is a style that I do not like. I prefer a style more like that of "mutt".
- I want a split view, so that I can see both the list of emails matching my query. A typical query is "unread".
- I want the split view to be the same for everything. I want to see an email tree in the index. Notmuch only shows one line with a read/unread count for each thread.
- Thread view. Both email readers pay attention to the email headers to figure out threads. (Lotus Notes thread support is completely borked. MS Outlook tends to get confused by threads. The result is that email conversations with corporate folks are more difficult. They fall into the "new mail in front, copy everything behind" mode because that's the only threading method that is reliable with these broken systems.
After trying notmuch and mu4e long enough to be reasonably expert I've switched to mu4e. The email reader is more important than the differences in tag and search. There may be a way to add index-only tags to mu4e with a lot less effort than changing the mail reader. I don't like modifying the original email. It feels wrong to me.
Switching back and forth was easy because they both use a maildir format for storing emails.