Earlier quoted context omitted.
This is where we're at too. We've long been evangelizing Mailchimp and Mandrill in our product, and as a result have sent plenty of customers their way. In fact, our product almost relies on them as a pair. Now, because of the ToS, we have to remove it from our product and port our users somewhere else...and fast. We also have to port our own servers to another service, and fast. I remember the day we finally had eno…
> We also have to port our own servers to another service, and fast. Once you've done that you should look at what other services you rely significantly upon and see about mitigating the risk there by having an alternative ready to go (or even sharing the load). At a previous startup we realised we relied wholly upon Mandrill and so reimplemented the sending code so that half of the emails went out via Mandrill and t…
This also has the benefit that if one service goes down, we can automatically fallback to the other with (hopefully) no downtime. Most email providers have a limit to what you can send until you're established with them, so using another provider as a standard backup isn't feasible, as suddenly sending 1,000's of emails a day will see the account get suspended pretty quickly.
Plus, if one of them goes out of business or changes their terms with little notice, like Mandrill, we should have a bit more time to work around it as at least one service will work.