I will assume your account is IMAP, most are. So moving a message from inbox to local folders is actually copying the message, deleting the original and notifying the server of that deletion. This is often made significantly slower if you use anti virus to monitor any of the mail ports, scan mail or scan the Thunderbird profile. While there are some truly horrible anti virus products out there, slow downs in the order of 40% are basically considered normal by anti virus vendors. So create an exception in your anti virus for the Thunderbird profile. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data#w_where-is-my-profile-stored Disable any spam or scam tracking identification etc in the anti virus package. (Some inject an add-on into Thunderbird ignoring Thunderbird settings) Disable any email scanning. Check the windows firewall is not set to do any connection checking. I notice my windows firewall developed a new "on" feature after a recent update that slowed things down. Some further diagnostic tools; *Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender. *Restart the operating system in '''[http://en.wikipedia.org/wiki/Safe_mode safe mode with Networking]'''. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: [https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode Windows 10], [http://windows.microsoft.com/en-us/windows-8/windows-startup-settings-safe-mode Windows 8], [http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-7 Windows 7], [http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-vista Windows Vista], [http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/boot_failsafe.mspx?mfr=true" Windows XP], [http://support.apple.com/kb/ht1564 OSX] ; If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

jmorgie, How did you do with Matt's advice?