I have skimmed the filtering sections of the manual.

Does xeams implement TMDA for challenge response?

.. Are my recipients [temp] whitelisted to avoid challenge response?

Can an ordinary user be enabled to view suspected message queues like the site admin?

Are spam assassin rules supported?

Is greylisting supported?

DNSBL informed rules?

When will there be DANE support?  RFC 6698

There should be rules to characterize headers as a single entity.  Size [is, less, greater], as char count.  And size filters for any individual header or X-header.

Is there DCC support? (Distributed Checksum Clearinghouse)

[I motivated cPanel to adopt DCC and many other great antispam ideas but they are no longer as responsive to ideas. BoxTrapper falls short of TMDA]

Don't waste money on Arvixe hosting or their infuriatingly substandard support for any class of service.