When comparing Postmark vs Mailgun, the Slant community recommends Mailgun for most people. In the question“What are the best transactional email services?” Mailgun is ranked 1st while Postmark is ranked 2nd. The most important reason people chose Mailgun is:
Mailgun is included and configured by default in Meteor.js. So for projects which are built using Meteor, it's very easy to integrate Mailgun.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Messages are unlikely to be marked as spam
Postmark is designed to send transactional messages. It specifically warns users not to use it to send weekly newsletter -- this way the emails sent by Postmark are less likely to be marked as spam, increasing the likelihood of your messages reaching the users.
Pro DMARC
Supports domain-based message authentication which helps to prevent spammers from using your domain to send email without your permission.
Pro Detailed analytics
Postmark offers very detailed analytics for your emails. For starters, it stores 45 days worth of email logs where you can search to find out which emails were sent, received, who received them, who read them and who marked them as spam.
There are also recipient profiles which keep track of everyone who gets your emails, complete with a list of messages that they have opened, deleted or marked as spam.
Pro Messages are Saved for 45 Days
All outgoing messages are saved for 45 days so you can see what you're sending to who. This is important if you are sending any dynamic content in your emails.
Pro Multiple server locations
Postmark has 5 server locations around the world (3 in the US, 1 in Amsterdam and 1 in SIngapore). This way emails will be sent fast regardless of where your users are.
Pro Integrates by default with Meteor.js
Mailgun is included and configured by default in Meteor.js. So for projects which are built using Meteor, it's very easy to integrate Mailgun.
Pro Developer-focused
Mailgun has a RESTful API with libraries and code examples in curl, Ruby, Python, PHP, Java, C#, Go.
Cons
Con Expensive
Postmark are one of the most expensive (if not the most expensive) services in the market, at $1.5 per 1000 emails.
Con Sub-par support
It has been reported several times that Mailgun's support is not excellent. Most of the time, they require a lot of time to respond to questions or support queries.