If the password of a mail user is changed via Parallels Plesk Panel, it is not propagated to the mailserver configuration. It is not possible to log in to this mailbox with the new password, and you receive the error "Login failed." Only changing the password via the administrator console of the mail server is valid.
ResolutionTo fix the problem, it is necessary to replace the MailName.php file with a new version as follows:
1. Rename the original MailName.php file in the "%plesk_dir%\admin\plib\mail" folder.
2. Download the new MailName.php file.
3. Copy the file to the "%plesk_dir%\admin\plib\mail" folder.