My suggestion then is to use a different password.

This is a Bug in the thunderbird Software, to user a different password is a temp solution, no a fix

passwort like 19@sEEs@60 with an gmx accounts does not works

Not really a helpful problem description. Please describe your problem in more detail:

• what you're doing,
• what happens,
• what you expect to happen.

I don't mean to complicate things, but I attempted to change my gmx account to that password and it isn't allowed by gmx.

I installed Thunderbird on a new laptop.

Then I tried to set up my account via IMAP.

I'm using a German @gmx.de email account.

I keep getting the message "Username or password incorrect."

IMAP was enabled at my gmx Account.

Logging in via the web works without any problems using this password. Feedback geben

Can you also post your Troubleshooting Information? At the top right of the Thunderbird window, click the menu button ≡, then select Help > Troubleshooting Information. Press the "Copy text to clipboard button" and paste the information into your reply.