Symptoms
Any options entered on Plesk, Server, Mail, Preferences page are not saved when OK button is clicked.Resolution
Please download the following file
http://download1.swsoft.com/Plesk/Autoupdate/Windows/8.3.0/130285/mailmng.exe
and place it to the %plesk_bin% folder
Note: Please see how to install Plesk hotfixes properly.
Additional information
%plesk_dir% is environment variable which points to Plesk installation folder. By default it is C:\Program Files\SWsoft\Plesk
%plesk_bin% is environment variable which points to Plesk binaries folder. By default it is C:\Program Files\SWsoft\Plesk\admin\bin