SageMailer allows customers to easily connect with their Amazon accounts and begin setting up campaigns/sending out messages on the first day. I felt the interface was easy to use and navigate, it connects with multiple Amazon marketplaces, and the templates are updated regularly to follow Amazon's constantly changing policies around messaging.

I switched to SageMailer because it had access to international Amazon marketplaces (I wanted to send emails to customers outside of just the US). However, after I switched, I was really impressed with the design of their templates, the ability to customize the templates, and the variety of settings available to set up your campaign. They stay up on the latest policy changes from Amazon so that you can feel confident that their templates are within policy. And best of all, they were cheaper than the vendor I had been using.