Hello! Congratulations on the new release. It feels very polished.

I am experiencing something that may be a regression (or a dumb mistake from my part). I can no longer search by tags using Kontact's "find messages". Indeed, my "Find Messages" dialog box is missing a "tag" option. Is that a bug of my particular installation, or is there a new way to find message by tags? Tags are a huge part of my workflow, and not being able to use it to find messages has been quite annoying. Thank you.

Search by tags is not fully implemented (see https://bugs.kde.org/show_bug.cgi?id=332511): in the mean time you can use the quick search bar to filter by tag, although it's just a stop-gap solution.