SendOut - Affordable email marketing for bloggers and influencers
Dynamic Campaigns by Sigstr - Share the most relevant content in every email
Mailblast - Email marketing on a budget using Amazon SES
PushMarket - Automate personalized emails for ecommerce (YC15)
Platformly - Platformly is a suite of tools for multi-channel marketing automation.
InboxSDK - First usable API to write Gmail Apps for 1B active users