Now that the holiday rush is behind us, it’s time to recap some fun research finds from 2012.

We’ve updated our research page, so check it out for any details I gloss over here. Let’s get started.

AOL and Hotmail readers spend more than Gmail readers

Using our eCommerce360 feature, users are able to track their customers from a MailChimp email campaign all the way to an order on their website. The user can then pass this order information back to MailChimp to keep track of their subscribers’ purchases and the return of each email campaign.

For MailChimp users conducting online retail, tracking purchases beats the pants off merely tracking clicks, so over the past year we’ve built up a lot of eCommerce360 data from those who are syncing email address purchase data back to us.

Well, we wondered if we could use this data to say anything about the spending habits of email addresses by domain. For example, do AOL users spend more than Gmail users?

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Let’s take a trip back to the heady days of 2009. Balloon Boy, Battlestar, Ms. Boyle. And, of course, MailChimp freemium. Three years ago, we allowed users to sign up for free accounts that they could keep forever. The effort has been a huge success, and these days we’re up to 2.5 million users. But when we first went free, the prospect really freaked some of us doomsdayers out. Wouldn’t we be opening the doors to the riff raff? How could we keep an eye on millions of customers to make sure no one was sending spam?

If even a few people got in the system and started abusing it, that could mean trouble for our reputation with major ISPs like Gmail, Hotmail, and Yahoo. No, we had to find a way to stop bad actors before they even sent a drop of email.

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MailChimp recently launched Wavelength, which allows users to find publishers like themselves and discover at a high level what other content their readership is engaged with. MailChimp has more than two million customers and sends more than three billion emails a month, so we’ve got all kinds of data in the Email Genome Project to bring to bear in understanding our vast network of publishers and readers.

But I wanted to find out if we could take Wavelength’s data one step further, one step deeper.

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The other day I wrote a post about subject line length and how it doesn’t influence open rates. But for most folks, open rate isn’t the issue—click rate is. And click rate arguably has something to do with subject line, and a lot to do with the content of your campaigns.

So the question is this: Once I’ve got someone looking at my campaign, what do the numbers say about how I should design my campaign?

The other day someone said to me, “You know who the best email marketers are?”

“Who!?” I asked with breathless excitement.

“The really bad spammers,” he said. “Their emails have a clear call to action and a single link. They’ve refined their communication through years of experience.”

It’s an interesting thought, isn’t it? To verify, we took a look at the bad users we’ve shut down over the years, thinking that surely there’d be a magic engagement number that all the good people fell above and all the bad people fell below. Much to our chagrin, the bad users we’d shut down regularly had better engagement than some of our good users. Uh oh. Maybe it has something to do with this campaign design discussion.

Are the spammers simple, lazy, or brilliant? Here’s a screenshot from my very own Gmail spam folder:

We have a clear subject line (although we know that ALL CAPS is detrimental to engagement). Then we get inside the email, and there’s no text, no pictures of some teary-eyed man suffering from ED. Just a single, Polish link. I know exactly what to do—click the link! Is this how email marketing should work? Is this what it takes to maximize clicks from those who open?

Let’s go to the numbers.
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We do a lot of interesting work on the engineering side here at MailChimp. We rarely talk about the infrastructure pieces (except when bad things happen, in the interest of transparency). The lack of information isn’t due to any sort of secrecy—we’re just busy. Lately we’ve noticed a rise in interest about how we approach scalability, so I thought it would be useful to post some information on the topic.

Today, I’ll share some high-level numbers and a brief overview. Going forward, we’ll get into the nitty-gritty details.

General Volume

We have millions of users, and we’re adding about 5,000 new ones every day. If you take duplicate emails across our users into account, it works out to billions of unique addresses (our customers’ customers) receiving our emails, opening them, clicking them, and being accounted for in analytics. Our MTAs send more than three billion emails to those addresses every month.

An average hour involves thousands of requests per second hitting our load balancers that aren’t absorbed by Akamai. Tens of thousands of queries per second bypass all cache and hit our primary database shards if you exclude all replication replay from the count. Most of those queries are background jobs and sending, not front-end request generated. Since a significant portion of our users are international now, we don’t really have slow time in terms of load.

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