There are two related parts to email marketing: making sure that your content is in good form; and making sure that it is actually delivered which is purely technical in nature.
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They are related in that all major email service providers (GMail, HotMail, Yahoo!, Comcast, Verizon, etc) scan email '''content''' on the receiving side with some heuristics to determine a 'spam' score in addition to other more 'technical' measures.