Last I checked Postmark is actually a fair bit more expensive, and SES is cheap and very, very, very barebones. After Mandrill exited the space in a fireball o

Last I checked Postmark is actually a fair bit more expensive, and SES is cheap and very, very, very barebones. After Mandrill exited the space in a fireball of burning good will, the remaining players in what I'd call the "full service but not eye-wateringly expensive" space are Sendgrid, Mailgun, and maybe Sparkpost, and there's not a lot of distance between them in terms of price and features. One thing Sendgrid is good at it letting people easily send emails (ie, receipts, confirmation emails, etc.) on behalf of their clients, while still passing SPF/DKIM checks, which Mailgun and Sparkpost make a bit harder. If you're working on a SaaS product that needs to send emails on behalf of your clients, Sendgrid is an obvious choice.