Mandrill Test Key Limit
I spent the greater part of an afternoon trying to figure out why I couldn't send an email with a test key in Mandrill (for the sticklers around, using a test key still tracks the email even though it doesn't actually send it). At first, I thought it was our system's built-in spam protection. Then I thought there was just a backlog (this is a test environment after all). I tried to send a few more test emails and noticed that our CRM was reporting that the emails were being rejected.
Again, I thought perhaps our mail sending service was rejecting them but it didn't look like it. So I searched for the test key in the Mandrill API log (I honestly didn't expect the search by key to work but it did). Lo and behold, there was every email I had tried to send rejected because of a "test-mode-limit".
At this point, I have no idea when the "test-mode-limit" resets and I don't even know what the limit is. I've reached out to Mandrill/Mailchimp for feedback.
Update: Mandrill got back to me and an entire account can generate up to 10 000 test sends per day. Daily sends reset at midnight unless you've already hit your daily test send limit, in which case it takes 24 hours before you can generate more test emails.