Syncronize Thunderbird tags between 2 PCs and with the phone app Spark (Outlook IMAP server)

Question

I have a laptop and a desktop both running Thunderbird. And a phone with the Spark app for emails. I have an Outlook IMAP account. I just need to be able to create the standard tag "to do" in either of the two Thunderbirds and have them saved to the server and not locally, in a way that I can see them in the other Thunderbird and on my phone. Now if I tag an email with the "to do" tag it does not transfer to the other Thunderbird. If I log in my Outlook IMAP account, I see no categories in my emails, while I have read that Thunderbird tags should correspond to Outlook categories. Any suggestion on how to do this?