About Email Firewalls

Email firewalls work like spam filters by regulating incoming email based on a set of rules established by the email server. Firewalls analyze email messages to determine if the message should be flagged as spam.

In this article, you'll learn more about email firewalls and what you need to know to help keep your sending reputation intact and your campaigns from getting flagged as spam.

How firewalls work

Email firewalls are set up to protect individuals or complex networks. They filter incoming and outgoing email-server traffic based on a set of rules determined by the firewall administrator. Not all email firewalls function exactly the same, but the main thing to know is that they monitor the behavior of other users on the server and communicate that information with other firewalls. When a subscriber marks your email as spam, that information gets shared with other servers, which can damage your sending reputation permanently.

Firewalls will denylist (other providers may refer to it as "blacklist") problem senders based on IP address and domain name. Because campaigns sent through Mailchimp use our servers, this means our reputation is also on the line. We take spam and abuse complaints very seriously and will take the proper steps to warn or suspend accounts as needed.

Maintain your sending reputation

The best way to avoid being flagged by email firewalls and spam filters is to keep your sending reputation intact. Put simply, always ask for permission to send emails. Here are a few basic pointers for good audience management and maintaining your sending reputation.

• Never send spam.
• Don't use third-party lists.
• Reconfirm addresses you haven't sent to recently.
• Assume you don't have permission if you're not absolutely sure that you do. Specifically ask people to join your audience and don't send emails to them through Mailchimp until you do.

Use clean content

Firewalls will also flag emails that contain suspicious content as spam. Here are some general pointers to be sure the content you send is clean and in compliance with anti-spam laws and Mailchimp's terms of use.

• Use Mailchimp's Campaign Builder to design a clean, clear email campaign.
• Always include your permission reminder and an unsubscribe link.