I am in the process of migrating from Thunderbird to eM Client. I have a number of tags/categories in Thunderbird, for example I have one for “receipts” and one for “2020”.
Tags that are only numbers (such as “2020”, “2021”, or “35”) do not show up in the eM Client interface. All the other tags do. If I modify the tag to be something like “_2020” or “2021x”, then they will show in emclient. It’s only the fully-numeric tags which don’t show.
If I make a tag within eM Client, it can be numeric, and there’s no problem. If I add the tag “2020” in emclient, it will sync to Thunderbird. If I add the tag “2020” in Thunderbird, it will not sync to emclient.