Blocklists

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A blocklist is a record of IPs and/or domains suspected of sending spam-like communication. These lists are managed by blocklist operators, and ISPs use their services to assess and categorize senders. In this article, we’ll go through what to do if you suspect you’re on a blocklist.

There are many different blocklists, of different size and reputation. As a sender of large emails batches, chances are that you’re intermittently going on and off blocklists without it noticeable impact on your marketing. Inbox Service Providers (ISPs) rarely label you as a spammer right away but may provide the benefit of the doubt on your initial listing. However, if you remain on a blocklist, your emails could eventually be classified as spam.

How do you end up on a blocklist?

One bad email campaign won’t put you on a blocklist. As always in email marketing, a consistent sending pattern is key. Also, it’s essential to keep a proper list hygiene and an ongoing analysis of your email communications.

Several factors can affect your reputation as a sender and potentially lead to blocklisting:

• Recipients marking your emails as spam.
• Sending messages to spam traps.
• Maintaining a high volume of send-outs with low engagement rates (such as open rates).
• Sustaining an unusually high bounce rate over an extended period.

Detecting if you're blocklisted can be tricky, but one indicator is a noticeable drop in open rates. Such a drop could also indicate that your emails are being diverted to folders other than the recipients' inboxes. In that case, ISPs may apply their own set of criteria to assess your sender reputation.

How do you get de-listed?

As mentioned, there are several types of blocklists, varying in size, usage, and impact.

Many times, you’ll be removed from the list automatically as your sender behavior improves (i.e., increased recipient activity, less complaints). Some of the larger blocklist operators have specific instructions on how to request a de-listing. In those cases, you must act accordingly.

There are tools you can use to monitor your listings, such as MX Toolbox and HetrixTools to name a couple.