Email has triggers, sequences, and dashboards. For years, direct mail had a spreadsheet and a print deadline. A good direct mail API closes that gap: your software decides who gets a mailpiece and when, and the provider prints, mails, and tracks it. The catch is that "best" depends on the job. A product team embedding transactional notices needs something very different from a marketing team running three-touch campaigns across dozens of clients. I compared Postalytics, Lob, PostGrid, PCM Integrations, and Click2Mail on the factors that actually separate them.