I'm trying to transfer around 30,000 emails from one account to another via Thunderbird. I've tried transferring a folder with around 10,000 emails in it by selecting all of them and running
Copy to >. The issue is, this cancels out halfway through, and leaves me to wonder which emails have and haven't been transferred since copying again will create duplicates (instead of skipping matches which would make sense). Then I have nothing but to delete them and restart.
Is there a way to transfer only ones that haven't been transferred? Or is there a way to simply force it to stop cancelling out?
I've bypassed this issue for now by selecting around 1500 emails at a time, and selecting by date ranges. However, now, after finally finishing the copy, I've discovered that a random set of the emails did not copy the attachments..?? When I try to open them, it says "This attachment appears to be empty. ..."
Is there a better alternative to email migration than Thunderbird? It simply does NOT work.