MailChimp

IP Address Ranges

To protect our overall deliverability, MailChimp uses hundreds of IP addresses. These IPs are grouped into different reputation levels. Which IP group your emails get sent from depends on your list's reputation score. We regularly monitor our IP acceptance rates using ReturnPath, a leading 3rd party deliverability vendor. Depending on which group of IPs email is sent from, inbox acceptance rates range from 96% to 99%. Just for comparison's sake, if you were to send your emails from your own servers, the average deliverability rate you could expect is roughly 56% (2008 ReturnPath Study).

ISP Feedback Loops

We're registered with all the major ISPs to receive alerts whenever your recipients report your campaigns as "junk" or "spam." These alerts that we receive are part of what's called "Feedback Loops." When that happens, 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, USA.net, Cox, Earthlink, and more.

Whitelists

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

Authentication

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 can add authentication to their campaigns free of charge, and by simply checking a box (unlike some other services, there's no server setup required). We support all of the major authentication standards: DKIM, SenderID, Domain Keys, and SPF. MailChimp is also a member of the Authentication and Online Trust Alliance (AOTA).

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 (there are roughly 30 different characteristics we've learned to look for) that can jeopardize our deliverability. The review team is empowered to suspend accounts and contact users about any risk factors they need to address.

Advanced Bounceback Sorting

When you send an email campaign, some servers will bounce your message back. When that happens, MailChimp analyzes the bounced message for code from the recipient's email server that will tell us if the recipient's email account is invalid (in which case we'll remove the recipient from your list automatically) or if the recipient's email account is temporarliy unavailable (in which case we'll automatically try to re-send the message later). If you do not manage bounces in this manner, most major ISPs will eventually block you from sending to them.

Industry Members

We stay abreast of industry and technology standards by being active members in email and ISP organizations such as the ESPC (Email Sender and Provider Coalition), AOTA (Authentication and Online Trust Alliance), MAAWG (Messaging Anti-Abuse Working Group), and EEC (Email Experience Council).

3rd Party Retention

We retain the services of a leading 3rd party deliverability vendor and a well-respected ISP relations consultancy to help us prevent, detect and in rare cases, resolve, any deliverability problems.

Inbox Inspector:

With one click, our users can scan their email campaigns for content and coding red flags that can cause deliverability problems. By preventing bad campaigns from leaving our system, we help our system's deliverability. More information

Email Deliverability

New to the topic of email deliverability? You should check out the "Deliverability" category of the MailChimp Blog:
Email Deliverability Topics

About MailChimp

MailChimp is an email service provider (ESP) that's been around since 2001. We've got over 275,000 users from all over the world (small business, big corporations, nonprofit groups, schools, churches, etc). Our servers deliver a few million emails a day, so we work very hard to keep the bad apples out, and to stay clean from abuse, to keep our overall deliverability high. Nobody's perfect, but we like to think we try the hardest.

Abuse Desk

Here's more information there about how we keep abuse off our system, and how we try to educate our users about proper email list management and etiquette:
http://www.mailchimp.com/abuse/