It may have happened to you but we never had issues with Mandrill in terms of deliverability for 2+ years. With Sendgrid, we have issues almost every week. Just yesterday, sendgrid had an issue and the CTO himself had to jump in with a post mortem. We had no choice but to go back to Mandrill because we cannot play with the critical transactional emails. Damn, email delivery is such a hard problem.
you might just not noticed but i would almost bet that it did happened to you as well. we noticed it after 1.5years of using mandrill. and only because one our user contacted us directly and was patient to cooperate with tracking the problem. after that we discovered plenty other cases. and communicating with mandrill revealed that it is how their system in fact works. anyways if you are happy with Mandrill good for you, but remember my warning: you are living in a dream that all the emails marked by mandrill as delivered are in fact delivered.
