That leads to a very interesting question… How are we doing?  After sifting through 500 or so IPs and crunching the numbers on over a quarter of a billion emails, I might have an answer.  There are graphs with colored lines and all kinds of explanations below, but within my data set one thing is true.  75% of the emails we receive are delivered within 5 minutes or less.  That’s pretty cool.

Begin Technical Babble

Before I throw the charts at you, it might help if we went over a few basics of how MailChimp delivery works.  When you send a campaign, your list is divided up and distributed amongst our shared IP pool.  Each IP has a FIFO queue for outbound emails, and the size of these queues directly affects your delivery time.

Clearly, we should divide your list evenly amongst all our IPs.  That would give us the fastest delivery time for sure.  Yep, it sure would.  It’d be really fast.  Are you getting the feeling we don’t do that?  Good, now let me explain why it isn’t the best solution.

At this stage, your campaign looks a lot like a highway.  One of the things we like to do is match your subscriber’s activity rating with the reputation of our IP.  We’re putting your best subscribers in the fast lane so they have the best possible chance for a successful delivery.  Of course, this means we can’t divide your list evenly.

If you’re wondering why we don’t send your campaign over all of our IPs, I have a simple answer.  “Hell is other people.”  I’m pretty sure Sartre would approve of me borrowing that phrase.

You see, every now and then we get a bad apple.  Sometimes it’s accidental and sometimes it’s malicious, but these rogue apples can get our IPs blocked.  By optimizing the number of IPs that any one campaign touches, we protect all of our users from the odd mushy apple.

More Complicated

This is where the highway analogy starts to get out of control.  Not only is your list divided among several IPs, but each IP has a separate connection for every receiving domain in its queue.  The receiving domain is the ISP your subscriber uses, like @gmail.com or @hotmail.com.  It’s worth taking a look at your list and noting which domains you send to the most.

The good news is that these connections can all send concurrently.  Of course, the ISPs themselves often throttle incoming email to their own preference.  You’ll notice in the charts below that one ISP in particular throttles heavily.

So it’s like there are different highways, but the lanes are kind of… No, it’s like each ISP is a different car manufacturer, and the speed limit is…  Okay, maybe if we all had flying cars and the toll booth was like a filter … Ugh, I honestly can’t think of a good way to picture this.  Feel free to make suggestions.

On top of all that mess, you’re not the only one sending a campaign.  Your emails are being queued along with everyone else who just hit the send button.  We do everything we can to minimize the queues, but there are certain times of day when our volume is off the chain.  It’ll make you think twice about the “schedule delivery” feature.

Actual Data

I took two weeks of data from our pool of shared IPs and added them up by hour.  The first chart shows the volume of emails we sent.  You can see our heaviest hours are between 9am and noon (EST), but from experience, that range shifts back an hour depending on the time of year.

The next few charts measure the time interval between when an email was queued and when it was accepted for delivery by the email provider.  Keep that last part in mind.  It takes two to deliver.  We send the email to the ISP, and they deliver it to your subscriber.  The first part I can measure.  The second part is anyone’s guess.

You can see that 85% of the emails queued between 10:00am and 10:59am were sent within 5 minutes of being queued.  For Yahoo, it took 45 minutes to deliver the next 10% (looking at the 95% graph).  To send the next 4.5% (looking at the 95.5% graph) of Yahoo emails took a whopping 285 minutes.  Yikes!

Notes

Why don’t you see a graph for 100%?  Well, it turns out that a lot of lists contain one or two addresses that don’t exist or can’t receive email anymore.  The way we figure it, there’s always a chance.  We’ll try to get the ISP to accept the email for up to three days, and sometimes it actually works.  It makes my charts look horrifying though, so I cut the numbers off at 99.5%.  Problem solved.

You may have noticed that Yahoo loves to throttle email.  If your list has a lot of Yahoo addresses, you’ll want to take this into account.  For those looking at the “All” line, it’s simply the sum of all the emails together.  As the percent completion goes up, the last few thousand emails tend to be heavily weighted with Yahoo addresses.  The “All” line reflects this by inching up as well.

I’m pretty happy with these delivery times. For most ISPs, 95% of the emails in our queues are sent out in 5 minutes or less. It says we’ve done a good job at balancing reputation and speed. In the second part of this series, I’ll go over all the stuff that happens to your campaign before it ever hits the queue. It’ll be a lot like going behind the scenes at Universal Studios. There will be flames shooting up out of nowhere and you’ll see that Freddie is an awesome robot.

Go to Delivery Speed, Part 2

He gave me some tips that I could pass on to our readers. So here you go:

• Comcast really, really hates it when you send to an old list (with lots of undeliverable email addresses). If you’ve got too many emails on your list that no longer exist, Comcast will block your IP address. This is a very strong argument for cleaning old, inactive members from your lists. Yes, I know it feels safer to keep old members on the list, because the number of recipients looks so much bigger. Yes, I know your boss keeps telling you not to clean your list, because they don’t want to lose any prospects. But those bad addresses are just holding back your overall deliverability and keeping the good addresses on your list from getting your message. Yes, I have numbers to prove it. In a later post.
• Comcast doesn’t like it if you send too many emails all at once to them (this one’s kind of a no-brainer). Here’s what makes them different: they’ll actually TELL you how many you’re allowed to send at once.
• As you can see from this chart, the rate of emails you’re allowed to send to Comcast at once depends on your IP’s “reputation.”
• Your IP reputation is based on at least two factors: Authentication (a technology standard that’s used to prove an email is not a forgery), and the IP’s “Sender Score” (Your IP’s Sender Score is kind of like a credit rating, and it’s the folks at ReturnPath who issue the score). MailChimp customers – Authentication is free with every MailChimp account, and through our relationship with ReturnPath we monitor our senderscore closely.

For those of you familiar with ISPs and abuse desks in general, none of this is all that new. The interesting stuff is how forthcoming and helpful Comcast is with their error codes and rate limiting charts. Overall, their new Postmaster site is one of the best I’ve ever seen (look at all the handy RSS feeds):

http://postmaster.comcast.net/

If you’re new to all this, and wonder how this applies to you:

• Don’t send to old email addresses. You’ll get yourself (and other innocent senders) blocked.
• At some ISPs, old email addresses get turned into spam traps. You send an email to a spamtrap, and you are instantly blocked. We had a case of a MailChimp user who sent to a 10-yr old email list (totally opt-in, and the guy luckily had IP/timestamps on all subscribers) and one of the addresses had been turned into a spam trap. The impact on his deliverability from a spamtrap hit was instantaneous and dramatic. Keeping his proof of opt-in for so long saved his behind.
• If you’re sending your emails from an ESP (like MailChimp, Constant Contact, etc) that has shared IP ranges, then one bad apple can truly spoil the whole IP range. So it’s important to go with an ESP that closely monitors their deliverability, and punishes bad senders (it’s for the greater good). Quality over quantity.
• Don’t export your entire email address book and assume they all want to receive email newsletters from you. Address book dumps are full of old email addresses, and are one of the most common reasons I see senders get blocked. Other reasons include: Fish bowls, sharing lists, and buying lists.
• If you have an old list of people who opted-in to receive emails from you, but you haven’t sent them an email in a really long time (or ever), then you need to delete any emails older than 1yr, then send the remaining subscribers a “remember me?” welcome email. Here’s a good example.
• If you send emails on a regular basis, and you think your system is cleaning the list for you, you still might want to segment your list by actives vs. inactives.

Comcast isn’t the only ISP that hates it when you send to old/dead lists.  AOL’s postmaster talks about IP reputation and undeliverables here. ReturnPath, the experts on email deliverability, mentions undeliverables here and offers some tips. Laura Atkins from WordtotheWise talks about “Letting Go” of old members.

In general, there’s a shift (again) in the way ISPs and email receivers judge emails as spam or not. Instead of relying on blacklists or focusing on bad content, they’re looking at your overall reputation as a sender. And list cleanliness (undeliverables, hard bounces, spam complaints) are huge factors in determining how clean your list is.

According to George Bilbrey, AOL, Gmail, and Yahoo have implemented DKIM email authentication.

For those of you who don’t know, authentication is a way to prevent email forgeries, and it can improve your deliverability. The AOTA says Authentication has hit its “tipping point.”

Since 2004, when email authentication started to really pick up steam, ISPs have been testing (and changing) their support for authentication. Some use one method for inbound, and another for outbound. Some support all methods of authentication. Some have abandoned it, or are in limbo. It can be confusing.

So we compiled a chart of which ISPs are using which authentication methods over here.

Of course, we’ve also made authentication “MailChimp Easy:” Our customers can authenticate their email campaigns with one simple click, and we cover all the major authentication standards (DKIM, Domain Keys, SenderID, and SPF).