Who is your email provider?

What is the size of your Inbox?

What is your anti-virus software?

My email provider is Pachosting, the email box size now is 5.5 GB, using the Windows Security as anti-virus software only.

Thanks

Whenever I log in this Thunderbird email acount, it keeps on downloading the message, it will last for one or two days sometimes until it finished the download, otherwise it will very difficult for me to write the email, I can write the email but writing every single letter also very slow......and even difficult for me to send out my email, also very slow....

Do you have any idea ? Thanks

Try to start Windows 10 in safe mode with networking enabled.

Does the problem go away?

Windows safe mode disables anti-virus software. This is a troubleshooting step, not a solution.

My emails had been finished downloaded after 2 days, so I cannot test it now, but it will be happened often, I will try the "Windows 11 in safe mode with networking enabled" next time, but it doesn't mean it can solve the problem, I guess.

Is it I have too many emails stored in the Inbox? But why it is only one email account will have this problem, since I have 3 emails account using Thunderbird.....

Accumulating a large no. of messages in Inbox is a bad idea. If you let your Inbox grow to a huge file, it would also take your anti-virus software a huge amount of time to scan your Inbox file every time a new message is received. Anti-virus software is the most likely culprit for slowing things down, or to even cause Thunderbird mail file corruption.

To avoid problems create an exception in your anti-virus software for the Thunderbird profile folder, so that the anti-virus real-time scanner will not scan it. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data#w_how-to-find-your-profile

Ok, thanks, I will try to do it.