Is this an IMAP account? Tags, I believe, are stored in the msf index. An IMAP account would repopulate the folders, and my guess is that caused the loss of tags. But I'm no expert on the topic.

OK, I sent the computer for service, I received it back, and had to set it up again. this time, I followed the instructions in the article, which said to copy the entire Thunderbird folder. The number of files and subfolders in the properties for the Thunderbird folder matched that of the source. when I started up Thunderbird, there were my emails, and my tag list, but no emails were tagged. I noticed a couple of errors saying that it could not find inbox minus one on the server. There is no mailbox inbox-1 on the server, but there is one in the profile that was working on the old machine. does Thunderbird store data anywhere else besides the Thunderbird folder in roaming? this is an IMap account, in case it matters, it’s a Hotmail account. Any ideas why my tags aren’t being moved? Thanks.

Well, I’m still mystified as to where tagging of messages is stored. It survives shutting down the program, so it has to be stored somewhere! :-) I found a way to move The tags. Here is what I have found out. I hope that it will help someone else. Since the starred state of messages is transferred, I starred the Messages containing a tag on the old machine, then filtered for stars on the new machine, and added the tag. First, save The state of any starred messages.

1. Press control+shift+k (filter) and choose starred.
2. Move to the message list and select the messages by pressing home, then shift+end.
3. Tag these messages with a new tag, say, starred.
4. With these messages still selected, press s to remove the stars.
5. For each tag, Display the messages containing the tag in the same way as in 1 above, Except choose tags and the desired tag.
6. Select these messages as in step 2 and press s to star them.
7. On the new machine, wait for the stars to appear. I think I speeded this up by going to the folder tree, moving to a different folder, and then back.
8. Display the starred messages as in step 1.
9. Apply the tag to them and unstar them.
10. wait until the stars are removed on the old machine, then proceed with the next tag.

After you have moved the last tag, use the starred tag to Mark the originally starred messages.

If not moving tags with the profile is not a bug, I think that this should be noted in the documentation of tags so that expectations of their use will be set correctly. I hope this helps someone.