MailChimp and Deliverability

You've probably seen a lot of email service providers advertise "98% deliverability" or "high deliverability" or "the best deliverability ever," and you might be wondering what it all means. Deliverability is a way to measure the success at which an email marketer gets a campaign into subscribers' inboxes. It involves anything that touches email delivery, like ISPs, MTAs, throttling, bounces, bulking, and spam issues. Senders affect their own deliverability, too—so if you create good content and maintain a clean list, your campaigns will be more likely to reach your subscribers.

The data varies widely, so you can see why deliverability is a complicated concept to wrap into a tidy little number. But you probably want to know MailChimp's success rate, so we've got charts showing specific deliverability histories for some of our high-volume clients.

Deliverability is more than numbers and charts, though. Here are the facts about MailChimp’s deliverability:

Omnivore is watching

We have abuse-detection technology that keeps our system clean by predicting bad behavior in a campaign before it even gets out the door. We compared more than 61 trillion data points, using a genetic pairing algorithm running on a cluster of EC2 servers, to create Omnivore. Our email genome project is constantly at work in the background, analyzing emails, absorbing new data, and preventing abuse on a massive scale. That means better deliverability for all MailChimp users.


Large corporations and financial institutions are constant victims of forgeries and phishing scams. In order to protect their reputation and prove their emails are "authentic," they use authentication technology in their email campaigns. Some ISPs are beginning to filter incoming email based on authentication. MailChimp customers will automatically have authentication added to their campaigns free of charge (unlike some other services, there's no server setup required). We support DKIM, SenderID, and SPF. MailChimp is also a member of the Authentication and Online Trust Alliance (AOTA).

Reports from ISP feedback loops and whitelisting

We're registered with all the major ISPs to receive alerts whenever your recipients report your campaigns as junk or spam. These alerts are part of what's called feedback loops. When we get an alert, we instantly unsubscribe those members from your list in order to keep you (and MailChimp) from being blocked in the future. We're on feedback loops with AOL, Hotmail, Comcast, Yahoo,, Cox, Earthlink, and more.

Even though most ISPs are transitioning to feedback loops, some still employ whitelists. MailChimp is registered with them and actively works to maintain our whitelisted status.

Human review team

We employ algorithms that scan our system for signs of abuse. But we also employ a human review team who can, in the blink of an eye, detect subtle cues about a user (we've learned to look for at least 30 different characteristics) that can jeopardize our deliverability. Our review team is empowered to suspend accounts and contact users about any risk factors they need to address.

Active industry members

MailChimp is part of the deliverability dialogue. We stay on top of industry and technology standards by participating in email and ISP organizations like the ESPC (Email Sender and Provider Coalition), AOTA (Authentication and Online Trust Alliance), MAAWG (Messaging Anti-Abuse Working Group), and EEC (Email Experience Council).

Dedicated IPs and warmup

To protect our overall deliverability, MailChimp uses hundreds of IP addresses that are grouped into different reputation levels. We base IP groups on list reputation scores, and we monitor our IP acceptance rates using ReturnPath. Depending on which group of IPs email is sent from, inbox acceptance rates range from 96% to 99%. Check out our IP address ranges right here.

We can send to extra-large lists, and we provide full authentication for those accounts to use their own domains. We know it takes some time to break in new IPs and make ISPs trust them, so we automatically warm up our dedicated IPs.