You can send and receive for an hour after opening Thunderbird?

And then you cannot send? Cannot receive? Both?

Then this message appears about entering a password and none of them match. If I give ignore, after some time the mail works again.

I probably cannot help much and so will hope that someone else joins the discussion. In the meantime, we can gather more information.

Based on my reading of many support discussions, I think that something may be interfering with Thunderbird's ability to store passwords. Do you have to enter a password when you start Thunderbird? Is it an account password or the "primary password"?

When you go to general settings - Passwords - Saved Passwords, then show passwords, do you see the passwords that you expect to see?

Do you use anti-virus software?

I finally received a massage:

The error message says: The message has been sent, but a copy was not placed in the Sent folder due to network errors or file access issues. You can try again or save the message locally in "Local Folders/Sent- ...".

You are having network problems. I don't know if that explains why you must enter your password often. I can imagine that it does. In any case, you'll want to fix the network problems first.

This thread may help: https://support.mozilla.org/en-US/que.../1493155