As always Plesk dont know anything about their product... also following stupid way to get some more money. Whatever.
Add MagicSpam Free to your Plesk server follow this steps please.
1) Download MagicSpam from Plesk page
MagicSpam Embedded Protection - Plesk Extensions (it says Plesk v17.9.0 and up... ya ya whatever)
2) Unzip it with WinRar or some other ZIP extractor.
3) Open meta.xml with text editor and find <plesk_min_version>17.9.0</plesk_min_version> line
4) Change it to <plesk_min_version>17.8.0</plesk_min_version> (or lower no different)
5) ZIP again
6) Upload file to your plesk server
7) Install it from SSH with this command: plesk bin extension --install /path/to/file.zip
Thats all. You are done.
Thank you.