I am attempting to use Thunderbird to migrate user "archives" from personal Gmail accounts to new Google Workspace branded accounts. The situation is: For many years, users were using a "hybrid" account for their work emails, so they could lean on Gmail's large storage on free accounts. They would use a personal Gmail account, collect emails, and "Send As" from them. They are now moved into a new Google Workspace environment. Users' personal email accounts could have a 50/50 split of work/personal email, and some have up to 10+ years and 50,000+ work emails. I have set up their source and destination email accounts in Thunderbird, and am using Incoming/Outgoing Search filters to identify their work emails (as there is a unique domain) and copy only those emails to their new work-only GW accounts. It is going into basically Archive>Inbox and Archive>Sent filters on the target end, and will not be mixed with current mail. The problem is the Copy function is breaking... a LOT. The first account I did worked flawlessly, but the second account would break when trying to copy mail. Even just 3,000 of them, or 1,500 of them. I can't tell if it's breaking because of sync interruptions, or because of mail-name-length-exceeding, or whatever reason. I am hoping there is a way to "keep copying no matter what" and auto-skip issues. Or if not, some way to put the client in the best condition to copy thousands/ten-thousands of emails from source to destination properly. The length of upload-sync time is not concerning. Just that the copy goes properly. (So for instance, is there a way to pause syncing and allow the copy to occur "local-only" first, in case the constant processing is breaking it.) Whatever is needed.