A. test for interference from other programs and features: A1. If on Windows, start *Windows'* safe mode with networking enabled - win10 https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode - win8 https://support.microsoft.com/en-us/help/17076/windows-8-startup-settings-safe-mode - win7 https://support.microsoft.com/en-us/help/17419/windows-7-advanced-startup-options-safe-mode#start-computer-safe-mode=windows-7 - XP https://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/boot_failsafe.mspx Still In Windows safe mode, start thunderbird in safe mode per https://support.mozilla.org/kb/safe-mode-thunderbird

Does problem substantially reduce or go away?

A2. If yes, things are better, then still in Windows safe mode start Thunderbird normally

• If problem is still gone, then cause is a program or feature loaded during windows startup. Possibilities include: antivirus SW, virus/malware, background downloads such as program updates - for more possibilities see https://wiki.mozilla.org/Thunderbird:Testing:Memory_Usage_Problems
• If problem is came back, then cause is likely a Thunderbird addon - identify by disabling them one at a time (or in groups) in Tools | addons | extensions and restarting TB

If problem is solved, please post details and mark this topic as solved

B. If problem persists

• empty Trash folder - right+click, pick Empty, confirm by right+click, Properties, and check "Size on disk"
• empty Junk folder - right+click, pick Empty, confirm by right+click, Properties, and check "Size on disk"
• reduce size of Inbox

If problem is solved, please post details and mark this topic as solved

C. If still a problem, please post more details.

Thanks very much. The problem has been solved. Windows and Thunderbird Safe modes with disabling add ons did the trick. Very grateful.

Please tell us, which addon(s) caused your problem? And you are OK now, with both Windows and Thunderbird *not* in safe mode?

I am very grateful for the resolution of the problem. But if you look at the web site which details the steps you have to take to discover what caused the problem you will see that it is a daunting task. Forgive me but I gave up at the scale of the task.

stuartzw said

I am very grateful for the resolution of the problem. But if you look at the web site which details the steps you have to take to discover what caused the problem you will see that it is a daunting task. Forgive me but I gave up at the scale of the task.

Thanks for the feedback. I will try to improve that. Note, the first few steps at that site are the most important

Bit late in the day, but I've found that just emptying my deleted, trash and junk folders has resolved the problem.