I'm a brand new Thunderbird user, having used Postbox for many happy years. I've been spending the last few days setting up a new profile, importing local mboxes, customizing settings, verifying downloads, etc. There were some hiccups but I felt most was stable (except for some stuck threading on a couple folders). I moved on to customize a few tags and setup a filter for tagging and that's when things got crazy. As soon as I moved to another message the tag disappeared. I've been trying to isolate the issue and searched and read a ton, but I can't figure it out because SOME tags stick! Mainly the first Important tag. I deleted and added a custom one and finally it stuck, but I couldn't add or edit any more. I made a whole fresh profile to just test the tagging and only Important works. I can see no difference between any of them in the config settings. I'm on a brand new Macbook Pro so it's up-to-date, my IMAP is icloud as it has been for over 20 years and I've always used tags in Postbox without issue, so I can't see how it's an .icloud server issue. I have only one email address, I don't sync across computers, environments, users, or installations. HOWEVER, I notice in my original profile where I imported my local mbox archives all the tags DO work there! So why do some unpredictably work on my imap and some don't? Anything else I can try? I can attach screenshots of anything if necessary. Thank you!!