There are a slew of transactional email providers out there these days (SendGrid, Mandrill, Mailgun, Postmark, AWS SES, ...).
What provider do you use? What do you like and not like about them?
Postmark. It just works and delivers.
I have heard others mention Postmark in the past. What's the big deal with Postmark? Why choose it and pay so much more?
Mailgun, hands down. Been using for years and I have no complaints with them.
I'd put that choice last, they are many and have very similar features for that.
If you use a stack that integrates with some better just pick that...
Like Amazon SES is a very raw email send.
Sendgrid do email list with auto schedule sends and such well.. (due many vendors have such features, I don't think AWS has that yet? Easy to miss, they put so much new stuff all the time..)
As you'd grow you might change providers, shouldn't be a major concern.
Any implementation experiences with SES?
I did it recently, and while it's cheap, it's not the most straightforward. Working with attachments has been tough and parsing the RFC 5322 format is a bit of a challenge with multi-part emails. I tried it after using Sendgrid on several projects--which I really like. I just wanted to see if SES was a cheaper alternative to Sendgrid.
sparpost / aws ses
ElasticMail. Pay as you go and descent delivery rates.