See https://support.mozilla.org/en-US/questions/1439493

it looks like using 'move through filters' works (slightly) At first I tried to move all but: "Applying filter Move to IMAP failed. Would you like to continue applying filters?"

So, just moved anything with my name in To address. That selected >5,000 emails and it started working. Though slowly.... Then it stopped at 200 with the same fail message. I selected the option to continue running filters and it uploaded one more then stalled.

I changed the filter to anything after 1/1/2022. That selected 300 email messages but immediately failed.

One pattern that seems consistent is if I find some way to transfer a few, the next try with that method fails.

according to the link above, I tried the method that installs an older version of TB, with the addon from github. First go moved about 200, then failed. Second go failed at about 900 :(

to make matters worse, the addon copies, not moves. So each go duplicated the emails and the originals were not sorting the same as the copied ones. So, I can't even use the few I got.

Praying for a miracle cure!

Just for fun, here is one of the fail messages:

Copy Complete - Copy Folder

Success

Copied 0 message(s) successfully, failed 23212 message(s) from: Local Folders/Local Archive to:

xxxxxxxxxxx@outlook.com/Archive2/Local Archive/Local Archive ABORTED!

Ok

X

A breakthrough! Perhaps this will help others and/or inform developers: I sorted all email in my local folder by email size and then moved smallest first, in batches. Though it failed once, it worked very well after. Allowing me to move thousands of email messages.

The good news is that my local folder with 35,000 messages is now down to 6,500 messages The bad news is that as soon as I started processing batches with email size over 25kb the move failed as before

The error TB notification reports is that the outlook.com server timed out.

So, I exported the remaining 6,500 messages as EML files (right click>save as) and will move them manually to the IMAP folder. (previously I tried <save as> EML for all 35,000 messages but that failed at about 8,000)

Though not as elegant as hoped, the problem is solved for me

If you have antivirus scanning mail, it might affect uploading ('server timed out') of large messages with attachments.

A breakthrough! Perhaps this will help others and/or inform developers: I sorted all email in my local folder by email size and then moved smallest first, in batches. Though it failed once, it worked very well after. Allowing me to move thousands of email messages.

The good news is that my local folder with 35,000 messages is now down to 6,500 messages The bad news is that as soon as I started processing batches with email size over 25kb the move failed as before

The error TB notification reports is that the outlook.com server timed out.

So, I exported the remaining 6,500 messages as EML files (right click>save as) and will move them manually to the IMAP folder. (previously I tried <save as> EML for all 35,000 messages but that failed at about 8,000)

Though not as elegant as hoped, the problem is solved for me

I think the original method of uploading with the add-on should still work as long as the bandwidth limits are obeyed: for gmail it is 500 MB per day, not sure about outlook.com. Maybe the best way is to break the upload into folders no larger than 500 MB, or the provider's limit, and upload one folder per day. The limit might explain why the process was aborted when attempted with large numbers of large messages.