Understanding Blacklists and More

It's important to understand blacklists and their impact on your deliverability. There are actually three important list types that you'll want to understand in relation to blacklists:

  • Blacklists
  • Greylists
  • Whitelists

Let's take a look at the different definitions and what you can do to avoid blacklists.



A blacklist contains IP addresses and domains that are suspected of sending spam. Many email servers and spam filters filter mail based on whether or not the sender's IP is on a blacklist. Ultimately, blacklists help to filter out spam and protect the recipients.


A greylist contains the IP addresses and domains of bulk senders. Greylisting can be used by receiving mail servers to temporarily reject mail coming from bulk senders. They can be used to deter spammers because most legitimate senders attempt retry the mail that is rejected while many spammers do not. Informz automatically retries temporary errors to deliver mailings.


A whitelist contains IP addresses, domains, and email addresses considered safe senders at the mail receiver or spam filter levels. This can help identify legitimate mail to be received without being labeled as "spam" or "junk." Keep in mind that whitelisting does not always prevent mail from being classified as spam. If mail is sent with patterns characteristic of spam, it is still very likely the mail will be filtered.

How Does a Sender Become Blacklisted?

A sender is typically blacklisted due to sending mail to spam trap addresses, receiving complaints, spikes/dips in volume, spam-related content, etc.

How Does a Sender Avoid Being Blacklisted?

Unfortunately, getting blacklisted is common and many times unavoidable. However, there are some things you can do to try to prevent future listings:

  • Send only to engaged, opted-in subscribers.
  • Send at a consistent volume.
  • Include a clear unsubscribe mechanism on all mailings.
  • Avoid common spam triggers (avoid third-party link shorteners, spam trigger words, image mapping, etc.).

What Do I Do If I'm Blacklisted?

Many blacklists are temporary and auto-delist. However, some lists require remediation, which Informz monitors. Remember, it is up to the email marketer to follow best sender practices and maintain a good sender reputation!