If you use EC2 or the like your IP address or the entire address block could have easily ended up on a spam list so your email will be blocked. I wish SendGrid was only necessary for people who sends lots of mail but the reality is that no cloy provider can guarantee that email from their IP addresses will be delivered.
We just switched off of SES because of the lack of bounce/rejection diagnostics, and their internal blacklisting policies are really aggressive. If someone's email server goes down for a few hours, they're blacklisted for quite some time, even after it comes back up.
After using SES for close to two years, I'd suggest looking elsewhere if you really care about deliverability or stats/metrics. We switched to Mandrill a few months ago and have been very impressed. It's still a tiny, microscopic percentage of our budget, but we get so much more (open/click reporting, sub-accounts, rendered email body history, much better blacklist/whitelist management).
> [...] the lack of bounce/rejection diagnostics [...]
My employer has been making more and more use of SES, and we've just started looking at automated processing of feedback notifications [1]. Did you find them lacking?
They get accurate data for clicks, but geolocation/browser stats for opens aren't 100%. They still track the rates, but it looks like they're coming from one of Google's proxies, so this is the best they can do for now.
