I have setup thunderbird to transfer 3 accounts emails to one new one in thunderbird but have run into some issues. It is roughly 400k emails across all accounts. IMAP is turned on in all the accounts. I have tried going to one accounts "All Mail" and selecting all and right clicking on that selection to copy them all to "All Mail" on the new account - I get a message that it is downloading all these emails again ( in the bottom left corner) though I don't see any emails show up in that new folder. When I try a single email copy it doesn't show up there either. I believe I am missing some sort of functionally ( IMAP or otherwise) that belies the UX instruction to copy an email from one folder to another. Also I tried setting up a local folder and doing the same, and no luck there either. In some instances I was able to get maybe 100 emails to move from one all mail to another though It was me trying this over and over and sometimes the number of total email would change to the right of "all mail" Ultimately I want to download all my email locally, copy all these local emails to the local sync path for my new email account and hopefully have those sync up to Gmail via thunderbird. Do I have this process misunderstood, are there limitations and how would this be possible through other means if what I describe is incorrect? the new gmail is setup to have the storage needed for these emails as well.