I bought sparkpost and they have some problem working with interspire which i got to know later. I asked them to give me time to fix things as i use interspire and you are the only one who need a patch to be added. Neither they refunded and keep billing me for no use. and nor they replied to my request. Handle with care.
I've tested every service on the list and I vote for Elastic Email.
Why isn't postmark in the comparison?
Thanks for great matrix. Have you got any comparison on SMTP.COM?
After going through send grid, mailjet, now happiest with mandrillapp
really easy to use