I learned a few things about the upper limit of MailChimp today. These are things that they don't make obvious, and really only effect you as you start to make use of Groups and List Fields. First, here's the skinny on Lists in MailChimp.

You probably only want to create a single list in MailChimp. If you need to create more than one list, and a person is on more than one of those lists, they will be counted as two people for billing purposes. So, be careful with multiple lists. Where we've found them useful is separating people that you don't want to send email at this time from the rest of your list. For example, if you currently don't do business with people from a specific country. You could add them to another list for safekeeping - then, if you ever start doing business with that country, you can tap that list.

So, now you've got a list. The next thing you'll want to do is add what MailChimp calls "Groupings". These are containers for collections of groups. We've used them for things like answers to a question (where each group contains people who answered a particular way), product families (where the groups are people that own a particular product within a product family), and special groups (like our beta testers or people participating in a sweepstakes). Here's the rub: you can only have 60 groups. Whether that is 10 groupings with six groups each or six groupings with 10 groups each. The total cannot exceed 60 groups.

Next, you have the concept of List Fields - these are items that are typically used as part of an API (application programming interface - fancy for connecting two applications together, like WuFoo and MailChimp). A List Field might be "Birthday" - enabling you to capture a person's birth date so you can send them a "Happy Birthday" email each year. This would be captured by a form in WuFoo, then passed to MailChimp for all the email action. Here's the rub: you can only have 30 List Fields.

In both cases, the allotment sounds generous, but once you get your email marketing campaigns rolling - you'll be surprised how quickly you approach those limits. There are strategies for setting up your data to maximize your opportunity within MailChimp, and plan for the day when you hit the limit - I'll save those for another blogging session!

Need a checklist to keep you from making a critical email marketing mistake when using MailChimp? Read this post.