As much as I like the simplicity of Postmark, their pricing makes it very hard for me to justify using their service. Sendgrid and Amazon SES are charging $0.10 per thousand. Postgrid is 15 times more expensive.
If your volume is ginormo this might not be the right solution for you. But as someone who simply needs the functionality and as minimal an install footprint/learning curve as possible this is really hard to beat. Hopefully my startup will take off and I will have to look long and hard at a replacement.
I'll point out that we have no "account minimums", only the $1.50/1000 email credits for both inbound and outbound that never expire.
Also, we're home to many happy customers that are sending very high volume - we offer them bulk-credit purchase rates as low as $0.50 per 1000 when buying 2MM credits at a time or more.
