Please note: if Thunderbird is closed - not running - then any messages that are received by the server are not downloaded. It's impossible to download anything if Thunderbird is not running. They just collect in your account on the server.

When you start Thunderbird, connection is made to server and then download occurs. So all emails received by server can only be downloaded when Thunderbird is connected to the internet.

I presume those emails are then looking wrong when you open to read them

See if something has gone wrong with the index file - try this:

• Right click on Inbox folder and select 'Properties'
• Click on 'Repair Folder' button
• click on 'OK'

That's right, when the program is turned off, it is not possible to download messages from the mail server. The problem is that after starting the program, messages downloaded from the mail server are unreadable. Only strings are displayed. Everything is fine on the mail server. After repairing the inbox folder the problem disappears but not for long. After a few days the situation repeats itself. It has been going on for about 2 weeks. Thunderbird is up to date. If it was a one-time situation I wouldn't write a problem report.

After repairing the inbox folder the problem disappears but not for long. After a few days the situation repeats itself. It has been going on for about 2 weeks. Thunderbird is up to date. If it was a one-time situation I wouldn't write a problem report.

https://bugzilla.mozilla.org/show_bug.cgi?id=1890230#c105 has a potential fix if you would like to try it and offer feedback.