Comment 4 for bug 204550

Activating the servers custom keywords let's this issue move away. But I don't think that the server has to support this feature. I also tried to get this working without this server setting and it works! But you have to circumvent it.

Normal copying/moving of messages around some existing IMAP folders doesn't remove the tags. This only happens for folders with no existing index file. Getting it to work is to open the newly created folder first before moving/copying the message into it. Than the tag doesn't get lost.

Also if the server uses a further index file to store custom keyword information we can enable that for servers which doesn't support this feature. What we should do is building the index file first if its not valid. And afterwards we can move/copy the tagged message. Would this be possible?