а дальше - какой-нибудь spamd, обучение спам - не спам и ранжирование по результату:
X-Spam-Score: 15.0
X-Spam-Report: Mail system is ......
Contact postmaster@.... for details.
Content analysis details: (15.0 points, 30.0 required)
pts rule name description
---- ---------------------- --------------------------------------------------
0.0 URIBL_RED Contains an URL listed in the URIBL redlist
[URIs:
inboxarmymarketing.net]
15 BAYES_99 BODY: Bayes spam probability is 99 to 100%
[score: 1.0000]
-0.0 T_RP_MATCHES_RCVD Envelope sender domain matches handover relay
domain
0.0 HTML_MESSAGE BODY: HTML included in message
0.0 T_DKIM_INVALID DKIM-Signature header exists but is not valid
X-Spam-Bar: +++++++++++++++ (15.0)
X-Spam-Flag: YES