Sugar Sell - Sugar Sell is a customer relationship management and sales automation software that can be used by salespeople, marketers, account executives, and support teams.
Squarespace Email Campaigns - Email, but pretty.
YetiForce CRM - Yetiforce helps companies best utilize free professional opensource CRM to lower costs and improve performance throughout the entire communication structure.
Lob - A simple API to integrate print & mail solutions into your applications.
Goldmine CRM - Goldmine CRM is a Customer Relationship Management software that helps you build and manage your contact list, send follow-up emails, track your results and build better customer relationships using customer data and insights.
PostGrid - Transform your Offline Communications. Use our fully-documented REST API to send personalized letters, checks, postcards and improve address accuracy.