Rspamd support
There is relatively new anti-spam tool - Rspamd. I think, it worth to be integrated with Plesk as an alternative to SpamAssassin. It shows better performance as the author says here http://rspamd.com/misc/2016/03/03/rspamd-performance.html

Thank you for your input! We will consider this functionality in upcoming releases, if it will be popular.
Everyone, please continue voting for this feature if you consider it important.
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IG
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Christian Heutger commented
I would welcome rspamd. SA needs very much tweaks (additional to post-greet and rbl tweaks on postfix) to get close: Pyzor, Razor(2), DCC, adjustable/addable different rulesets, special plugins, GeoIP filtering, bayes could be fed with spam by spam archives like http://artinvoice.hu/spams/, should be tweaked by KAM rules etc. Look at my post on Proxmox Mail Gateway which is an antispam gateway, but also need tweaks. Great would be to have all of this in Plesk. A global bayes database for all Plesk users may help.
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H.K commented
SA could be made better with adding global bayes database support, Pyzon etc also.