Managing a yahoo email account via Thunderbird (158.0) and IMAP - moving large number messages

not what you are asking really, but have you tried copying and subsequently deleting the emails from the inbox? .The transfer process happens in the background, given how slow most domestic internet connections are with regard to uploads most of us would despair just waiting otherwise. But that introducess a whole host of silent failures that can happen and with Yahoo you can expect at least some. This inherent issue is exacerbared if you have an antivirus product scanning email or in some cases encrypted connections. It just slows an already slow process. Then things just start to timeout, the connection gets dropped and despite everyones best efforts things get "forgotten" You could monitor the actual activities closer using the activity manager (double click the status bar on the bottom of Thunderbird main windows) or the error console (although I would recommend clearing it before starting a move, if get quite noisy in there just fetching mail. but it does flag error for which you will not otherwise see an error message. Finally there is logging.https://wiki.mozilla.org/MailNews:Logging#Gecko_Logging You could create a log of the entire conversation that occurs up to the point of failure so we can look at exactly what the real error is. The log will be large (quite large in a short time) as the entirety of each message is included as the thing moves beck to the new folder on the server so I would not suggest trying to post it in a message in a public forum. If you should go the logging path, I will give you an email address to send the last part of it to. I certainly do not want to look at any more than I have to to diagnose the issue, but I would guess in the initial phase it will be a timeout. Not that if you use the now popular Export server name for Yahoo that Yahoo do not apparently support upload synchronization despite that being part of the IMAP standard. So you might be playing with a broken bat and an odd shaped ball. Unfortunately concrete information about Yahoos export server is not readily available from Yahoo and the internet is full of user assumptions and investigations that make valid or otherwise conclusions. This stuff is a mess of epic proportions really.