Marketo can dedupe data and nurture leads; an ESP can host landing pages and provide email open rates.

Marketo can score and nurture leads; an ESP can send multi-step campaigns and track open and click rates.

Marketo can measure the impact of marketing initiatives on revenue; an ESP can track open and click rates.

Marketo has the ability to send personalized emails and monitor website actions; an ESP can send email blasts and score leads.