After entering a wrong IMAP password, the login is irresponsive, nothing happens

Dovecot tracks login failures and delays logins after a login failed. This is a feature called Authentication Penalty. You can check the current penalties with

doveadm penalty

IMAP login fails with Thunderbird when password contains non ASCII characters

The IMAP protocol originally only allowed ASCII characters to be used for passwords. Most servers and clients support UTF-8 by now. Thunderbird 1 still transmits the password in ASCII. Because of this the hash Dovecot makes differs from the UTF-8 version of the password and Dovecot rejects the password, yielding a "Password mismatch" error.

Possible solutions are:

  • use a different mail client
  • only use ASCII characters in passwords

  1. Observed with Thunderbird 52.8.0.