For years when I shop online I have been manually moving order confirmation emails to a Local Folder called "Orders" so I can search them do e.g. reorder items. When I began using Thunderbird as a Gmail client, I continued the practice. But this isn't a Gmail-centric way of doing things, and I can't search my Thunderbird local folder when I'm accessing Gmail remotely on my phone. So going forward I want to add the Gmail label "Orders" to each order confirmation email. But what do I do with my legacy Thunderbird Local Folder messages? I need some way to tell Thunderbird: 'For each message in this Local Folder, tell Gmail to label it with the Gmail label "Orders"'. Is there an easy way to do that? If not, is there some way I could harvest the Message IDs of the messages and run some script (perhaps one I have to write myself)? There are >2,000 messages in the folder, so doing this by hand one-by-one is simply not a viable option. I'm happy to roll up my sleeves and do some scripting work though. Thanks for any advice, even if it is just "you're out of luck". :)