Postmark is a reliable transactional email service provider that offers blazing-fast delivery, outstanding customer support, and straightforward documentation. It separates promotional and transactional emails to protect high deliverability, has transparent pricing, and includes pre-built templates for common types of transactional messages. Postmark's pros include reliable and lightning-fast delivery, promotional and transactional email separation, 45 days of data retention by default, and transparent pricing. The cons are a narrow focus on transactional email only and no list management or marketing automation features out of the box. Pricing starts at $15/month for 10,000 emails. Amazon SES is an extremely inexpensive option with global reach but lacks support, deliverability insights, and requires manual work to set up some functionality. SendGrid offers a powerful all-in-one service with customer engagement tools and marketing automation but has mixed deliverability results, pay more for better service, and frustrating customer support experiences. Mailgun provides reliable service with a 99.99% uptime SLA and focus on transactional email but has inconsistent deliverability and sending speed issues, mixed customer support reviews, and requires manual work to set up some functionality. MessageBird offers compliance and enterprise support but is focused on the enterprise market, has a complex feature set, and mixed customer service responses. Mailchimp Transactional offers an excellent "everything service" with strong analytics but is part of a larger ecosystem, comes with additional costs, and may not be the best fit for non-Mailchimp users. Postmark stands out as the top choice due to its reliable delivery, ease of use, responsive customer support, clear pricing structure, and robust email analytics data.