When trying to login to Horde webmail with a valid username and password, the login fails with a message that the login details are invalid:
Login failed because your username or password was entered incorrectly.
IMAP support was disabled in horde config.
~# grep imap /etc/psa-webmail/horde/horde/conf.php $conf['imap']['enabled'] = false;
Activate Horde IMAP support
~# echo "$conf['imap']['enabled'] = true;" >> /etc/psa-webmail/horde/horde/conf.php