What is your anti-virus software?

I run Malwarebytes Premium as my main virus program. This has been going on for about 2 months, prior to my getting this virus program in. Before, it was a couple of freeware programs.

Is there some sort of processing done on the emails? Would I need to turn off the virus programs?

Lets see, is this IMAP or POP. My guess is imap.

So your select thousands of email and select delete. Thunderbird goes of to the server and asks that email XXXX be deleted. Server replies that email XXXX has been deleted. Server copies email XXXX to the deleted folder and notifies the mail client that a new mail is in the deleted folder Thunderbird updates the storage file that the mail is now deleted. The anti virus starts scanning the mail store. (at around 1 GB per 10 minutes this might be slow.) Thunderbird updates the deleted folder. Anti virus stats scanning that. Next mail. Ohh the scans are still going. I do not know if the AV doggedly continues when the cycle is repeated in a fe nano seconds or if it restart or what. Mail folders are both still locked by the AV , so at the very least updates will slow down.

How long is this going to take you think? Before something trips over it's own toes. In your case a couple of hundred it would appear.

Now lets factor i internet connection speed. Most people are connected with a fairly moderate upload speed. For example Comcasts economy is 768 Kbps. As there are 8 bits in a byte that is 768 byte per second. As IMAP is a relatively heavy user of that available upload bandwidth things coke up fairly easily in the pipe. Especially if someone else in the house is using the internet for gaming.

So we are fighting the dual issues of lagging data and difficulties in accessing file storage.

Without being to pointed about it. If you have that many mails to delete, delete them on the server.

Matt said

Lets see, is this IMAP or POP. My guess is imap. So your select thousands of email and select delete. Thunderbird goes of to the server and asks that email XXXX be deleted. Server replies that email XXXX has been deleted. Server copies email XXXX to the deleted folder and notifies the mail client that a new mail is in the deleted folder Thunderbird updates the storage file that the mail is now deleted. The anti virus starts scanning the mail store. (at around 1 GB per 10 minutes this might be slow.) Thunderbird updates the deleted folder. Anti virus stats scanning that. Next mail. Ohh the scans are still going. I do not know if the AV doggedly continues when the cycle is repeated in a fe nano seconds or if it restart or what. Mail folders are both still locked by the AV , so at the very least updates will slow down. How long is this going to take you think? Before something trips over it's own toes. In your case a couple of hundred it would appear. Now lets factor i internet connection speed. Most people are connected with a fairly moderate upload speed. For example Comcasts economy is 768 Kbps. As there are 8 bits in a byte that is 768 byte per second. As IMAP is a relatively heavy user of that available upload bandwidth things coke up fairly easily in the pipe. Especially if someone else in the house is using the internet for gaming. So we are fighting the dual issues of lagging data and difficulties in accessing file storage. Without being to pointed about it. If you have that many mails to delete, delete them on the server.

Ok, well I would only try 1000 or so at a time, but I see your point! I'll try that. Thanks.

Seriously, just see how it goes in windows safe mode with networking... you will almost certainly do better. Faster if not getting more at one go.

I will suggest you do batches of less that a thousand regardless. Thunderbird has anecdotal issues once you go much past that with loosing the plot itself.