Resolution
If you need to use spell checker in your horde webmail follow the instructions below. But note that this is only example, you can use another folder for aSpell installation:1. Adjust horde to use aspell. Insert the line
$conf['utils']['spellchecker'] = 'aspell';
to "%plesk_vhosts%\webmail\horde\imp\config\conf.php"
2. Download full installer from
http://aspell.net/win32/
3. Install it to C:\aSpell
4. Grant read permissions to user IUSRPLESK_horde on this folder to let horde be able to achieve it.
5. Add C:\aSpell\bin to Windows system variable Path.
You can do it from
Control Panel > System > Advanced tab > Environment Variables > System variable section > Edit variable Path > Add the line ;C:\Aspell\bin to the end of existing line.
6. Restart the server to apply the change.
7. Download the dictionary corresponding to your language from the same web site. You can install several dictionaries.