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Revisiting Deliverability

Deliverability is more than just an industry buzzword — it’s a way to measure the success at which an email marketer gets a campaign into subscribers’ inboxes.

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One of our Agency Partners once told us that new clients who switch to Mailchimp often ask her why their email stats have changed. We thought a refresher on how Mailchimp does deliverability might give our agencies some helpful talking points. Bonus: We have a Q&A with our VP of Operations, Joe Uhl.

In email marketing, permission is key. It’s an important element of our Terms of Use, but it all ties back into deliverability. When you send to people who asked for your email, you get fewer spam complaints, higher engagement, and a better overall sending reputation.

Deliverability is more than just an industry buzzword — it’s a way to measure the success at which an email marketer gets a campaign into subscribers’ inboxes. It involves every facet of email delivery: from the technical stuff like ISPs, MTAs, and throttling, to the aspects that you (and your client) can control, like the cleanliness of a list or an email’s content.

Here’s how Mailchimp does deliverability.

Someone looking at servers on a rack in a facility

Getting to know the client

Mailchimp has millions of customers who send billions of emails every month to recipients all around the world, so it’s crucial that we have the infrastructure and resources to support that type of volume. For 15 years, as we’ve been developing products that empower businesses, we’ve also been working hard to build out a secure, reliable infrastructure behind the scenes.

Today, we’ve got thousands of servers in world-class data centers. Plus, we’re constantly scaling to prepare for the future. But deliverability isn’t just about hardware like servers, switches, load balancers, and ethernet cable. Here are some of the other ways Mailchimp works to ensure deliverability for your clients:

  • We’re a member of a number of different industry-wide organizations (ESPC, AOTA, MAAWG, and EEC) dedicated to deliverability and maintaining the email ecosystem. This allows us to stay up to date on the latest industry and technological standards, so we can provide the best possible service to our users.

  • You’re probably familiar with the ways Mailchimp handles spam complaints, but you might not know that ISP feedback loops and whitelists are a driving force behind that behavior. We’re registered with all of the major ISPs to receive alerts when a campaign is marked as junk, so we can automatically remove the recipients who’ve filed complaint from your clients’ lists. This helps to prevent a recipient from submitting multiple complaints, which can harm deliverability and lead to future emails landing directly into spam folders.

  • We’ve developed our own abuse-detection technology that analyzes campaign data and user activity to predict — and prevent — bad behavior in campaigns. Omnivore prevents abuse on a massive scale, which helps us uphold our reputation and improve deliverability for everyone. We also have a human review team that monitors for potential abuse and is empowered to suspend accounts and contact users about risk factors that need to be addressed.

  • Authentication acts like a license plate for an email — a trackable identifier that proves to a recipient’s ISP that the email is coming from a legitimate sender. Mailchimp automatically adds DKIM and SPF authentication to all campaigns by default, so you won’t need to edit DNS records manually. But if you’d like to set up custom authentication for your clients, you can do that, too.

Mailchimp delivers email very fast. We send over a million emails per minute in peak hours, and the average user campaign sent to 1 million emails takes 45 minutes. But major ISPs place limits on the number of emails that can be received from an IP address in any given amount of time. Those limits are unpublished, and can be affected by bounce rates, abuse complaints, subscriber engagement, spam trap hits, or any other behavior an ISP deems suspicious. Mailchimp has hundreds of IP addresses. They’re grouped by list reputation scores and have inbox acceptance ratings of 96%- 99%. That’s how we send through multiple IP addresses and account for throttling.

Deliverability Q&A with Joe Uhl

Joe Uhl is the VP of Operations at Mailchimp. He leads the teams that support the entire company — operations, delivery, IT, facilities, and office management.

We sat down with Joe to chat about deliverability, infrastructure, and what sets Mailchimp apart.

Joe, should agencies be concerned with an ESP’s infrastructure?

Yeah, I think it matters a lot, and there are a bunch of different pieces to it, too. Is the ESP reliable? How often do they experience downtime? Are they transparent about it when they do? Here at Mailchimp, we try to be as transparent as possible. We have a status page that’s constantly updated with raw monitoring data, and we take uptime very seriously.

It helps that we’re as big as we are, because we’re able to identify a lot of good patterns. It’s provided the opportunity for us to develop the building blocks that we needed to be able to scale as we have. We have thousands of servers, our own fiber loops, we’re in several of the carrier hotels in Atlanta — we’ve built up a serious infrastructure that you couldn’t just go get if you were falling behind.

What sets Mailchimp’s infrastructure apart from other ESPs?

Infrastructure-wise, we actually do a lot of things differently. Many competitors use big, third-party vendors, but we buy our own servers, use open-source software, and keep all of the expertise in-house. It helps us move faster. I’d rather find an expert and hire them to work here at Mailchimp than flush that money away on a consultant somewhere.

For some companies, if they wanted to do a feature shift, for example, they would need to plan and coordinate with those third parties to make sure they had a big enough database. We don’t have that type of limitation. We’re unusual in the ESP market because we’re built more like a Facebook or a Google in terms of how we shard and stack. Our units of infrastructure are pretty small. There are no single points of failure in the way we build things because we’d rather spread everything out. If we want to iterate, or react, we can just order more servers and do it. We don’t need to go through anyone else.

How is Mailchimp’s approach to delivery unique compared to other ESPs?

In many cases, when other ESPs talk about their delivery team, they’re really talking about account reps that work with customers and coach them on best practices. Our approach is different. It’s much more technical. It’s all about data. We’ve got good relationships with all the major mailbox operators. On the technical side, it’s a constant arms race — as the spammers’ tactics evolve, so do the rules and requirements across all of the different mailboxes. We’ve got to pay close attention to things like Reverse DNS, DKIM, and SPF Records. Our delivery team also has to track and maintain thousands of different provider rules too, things like how many IPs we can use, how many connections we can have per second, how many messages per connection, and how long a connection can be held open. It’s all constantly evolving, so you’ve got to have a really good team that stays on top of everything and is constantly monitoring for the slightest changes. I think we’re really good at that.

Do you recommend that agencies invest in dedicated IPs for their clients?

There’s a lot of bad advice out there about sending email. Sometimes, people feel that they have to have a dedicated IP to get good delivery. The truth is that, in most cases, they’re better off just using our shared IPs because they’re older and they’re even more reliable. We care more about reliable delivery than we do about selling IPs. When you start getting to lists with hundreds of thousands of addresses, a dedicated IP can make sense, but for most folks, they can actually see better deliverability with our regular IPs.

How does Mailchimp’s deliverability compare to smaller ESPs?

It’s all about scale. As an ESP grows, it becomes more difficult to keep up with that growth.

If you’re small, you can make it for quite some time, but it’s not always sustainable. We’ve grown into one of the biggest ESPs now, and we’ve gotten to the point where we’ve been able to build good relationships — and a good reputation — with many of the block list operators. They respect us and are willing work with us if we get in a jam because they know we take reputation seriously and are willing to enforce quickly.

The other big difference is that we’re far more strict about what we will and won’t allow in our system. We don’t allow affiliate marketing, we don’t allow adult content, and we’re very strict about the permissioning of the list. We’ve been really consistent in that stance over the years, and as a result, we’ve had to say no to some huge companies. We put more value in having a clean reputation than we do in generating revenue, and that’s been our stance since the beginning. But it’s paid off for us, and it’s helped us develop those good relationships I mentioned earlier.

Should an agency be discouraging their clients from importing a list into Mailchimp?

It depends on the list. We trust people, so we won’t stop anyone from logging into Mailchimp and importing a list. But we do a lot of sampling and prediction on each list, and we’ll shut it down if we think it’s going to perform poorly. And we’ll watch when folks send too, so if someone sends and it doesn’t perform well (maybe it generates high bounce or abuse rates, for example), we’ll shut that down, too. These policies do mean that we’re not always able to serve some of our potential customers, but in the long run, it helps all of our other users have more success with their own deliverability.

If you ran your own agency, what questions would you be asking potential ESPs?

I’d want to know how they monitor uptime, and how they handle incidents. How do they know when something is wrong, and, in turn, how do they show that to their customers? We just throw our uptime numbers on the status page. Most companies will have a grid of services and dates with a red/yellow/green and, when the incident is resolved, they’ll just flip it back to green so there’s not a public, historical record of the issue.

I’d ask about their infrastructure. Will I be able to track how things are going and what will they do when there’s an outage? How have you built your app? What kind of storage, networking, and servers do you use? What kind of people do you have?

3 tips to help your clients avoid spam filters

Building and maintaining a clean list is essential for any email marketer, but it’s only half the battle. You’ll also need to keep emails out of the spam folder. These tips can help:

Be mindful of content, code, and formatting.

Some spam filters will flag emails based on content or images. There’s not an all-encompassing set of rules you’ll need to follow, but it’s important to keep your client’s campaigns clear and focused. Design (and personalize) emails to promote engagement. If you’re building custom templates for your clients, make sure they don’t contain extraneous code, extra tags, or code pulled in from Microsoft Word.

Stay on brand.

Work with clients to identify the aspects of their brand that resonate with their audience, and then develop an email marketing plan with that in mind. Stay consistent with the content, tone, and design that’s present across the client’s website and social channels — you’ll help create a cohesive brand identity for your clients and their audience. Subscribers will be more engaged, leading to a healthier list and improved deliverability.

Test, test, test.

Subscriber engagement (and deliverability) can improve when your clients send their best email at the best time. A/B and multivariate testing make it easy to try out different elements of an email, so you can quickly determine what leads to higher levels of engagement. Or, use delivery tools like Timewarp or Send Time Optimization to get the campaign to subscribers at just the right time. And you can always preview and send test versions of an email to make sure everything looks great before sending to subscribers.

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