My MailChimp account actually got banned due to limitations in their AB testing framework. At the time at least, they had no proper way to segment cohorts, mea

My MailChimp account actually got banned due to limitations in their AB testing framework. At the time at least, they had no proper way to segment cohorts, meaning that in order to control for things like length or circumstances of subscription, we had to do multiple smaller sends to lists that were subsets of our subscribers and aggregate the testing data afterwards, rather than being able to do just one send. On top of this creating a lot of extra work setting up the sends, it skews the statistics on things like SPAM complaints. What caused the account to be banned was that some of the smaller lists would occasionally see spikes in SPAM complaints. These spikes were well within statistical norms. However, because MailChimp will ban an account that breaks a threshold of complaints for a single list in a single sending, we triggered the ban, despite the list and send as a whole, being well within their limits. Had the AB testing framework been built properly, to account for cohorts, we would have had no issues. I tried to speak with their CS to explain the issue, but it seems either they could not understand or weren't interested. All of this, after multiple communications with their tech team about the limitations of their frameworks and how they could improve their AB testing. If you are looking to do anything beyond incredibly basic AB Testing, I would look elsewhere. We ended up at SendGrid, though my recent issues with their billing prevent me from recommending them either.