Email Delivery Services Assessment

Useful sources of information:

After some research, I decided to initially focus on three services.

Criteria	Mailgun	Sendgrid	Postmark
Free emails	10,000/mo	12,000/mo	First 25,000
Credit Card (CC) required	No	No	No
Next tier	500,000 emails; $0.00050/email	40,000 emails; $9.95/mo	$1.50 /thousand emails
Next tier price - 10K emails	$5	$9.95	$15
Next tier price - 40K emails	$20	$9.95	$60

As a result of pricing review, I decided to focus on just Sendgrid and Mailgun.

Criteria	Mailgun	Sendgrid
Documentation	Extensive	Extensive
Reporting	Extensive, 7 days	Extensive, 7 days
Test support (API)	Yes, emails accepted but not sent, no charge for emails.	We do not offer a true “sandbox” environment
Availability	Can't find long-term stats. Operational status and incident history available.	Can't find long-term stats. Operational status and incident history available.
Incoming email	Routes (ala Rails) can be defined, and email can be sent to app via HTTP or forwarded to another address. Routes defined via control panel or code.	Can parse incoming email and deliver via POST to specified URL. (limited to one such URL).
Other features of interest	jQuery plugin provides email validation for forms, including format, DNS/MX lookups, support for provider grammar (e.g. gmail: myaddr+sometag@gmail.com)
Comments	Notable in that all features are available to free accounts. Also, clearly focused on 1) developers, and 2) transactional email, and not trying to compete in the marketing email space.

All services support sending email via SMTP or API.
All services support push notifications via web hooks (e.g. email delivered, opened, etc.).

Based on (admittedly quick) review of all criteria, against our current and prospective needs, it appears that Mailgun is the best fit for PETS.