Are you talking about a POP mail account? 'Account Settings' > 'Disk Space' for account "To save disk space, do not download:" Below that text is the checkbox 'Messages larger than X kb' where you set the size as well. I presume you selected that checkbox and set a size. What size did you set - it helps when you need to look for the info below?

Settings > General scroll down to bottom click on 'Config Editor' button Advanced Preferences opens in a new tab In search type: .max_size There should a default which you ignore

• mail.server.default.max_size

look for lines like this where line same but with a different server number: examples:

• mail.server.server1.max_size
• mail.server.server2.max_size

They should have a value of whatever you set. For any of those lines with server number - click on the far right delete/trash bin icon. When you have trashed them - they now have a strikethrough line. Exit Thunderbird wait a few moments and then restart Thunderbird. It will completely remove them and update preferences properly and should reolve the problem.

I did choose the option like you and then later unchecked it. I expected those Advanced Preferences to be removed auto matically and was surprised to they still existed - so I removed everything via the above method. This maybe something to get reported as a bug, so I'll check to see if it's been previously reported.

Created a bug report - you can follow it here: https://bugzilla.mozilla.org/show_bug.cgi?id=2030969

Can you offer some info so I can forward it into bug report. What version of Thunderbird are you using? what OS eg: Windows, Mac, Linux ?

Yes, this worked. The lines were there and I removed them. Apparently the checkbox sets the function but unchecking the box does not remove it.

I'm using 140.9.1esr (64-bit) with Windows 11.

An update - this did not solve the issue with all my email accounts. Just one. The primary account still fails to download the entire message the first time. There is no max_size in the config file anymore.