5 ways to avoid landing on an ISP blacklist

ISP blacklist : also known as an email marketer's worst nightmare. Landing there means that you've been labeled as a spammer and are blocked from sending.

Hermes thinking about spam

ISP blacklist: also known as an email marketer's worst nightmare. Landing on a blacklist means that you've been labeled as a spammer and are blocked from sending. It can be tough to get yourself off the list, affect your reputation with customers and cost you revenue.

According to Return Path, a surprising 20% of businesses in the U.S. have been blacklisted.  These are “white hat” email marketers who are not intentionally spamming customers, rather they’re sending relevant content to an audience that has expressed interest in receiving communication. Now why would they get blacklisted? ISPs have strict algorithms built to catch spammers, but sometimes legitimate senders get caught in the filter when testing out new techniques or if their security is compromised.

Most interesting of all, marketers are most likely to be blacklisted during the holiday season (November - December), since promotions are more frequent and marketers feel pushed to be more aggressive in their messaging.  Here are some points to keep in mind, especially as you are gearing up for the holidays, to help avoid landing on that dreaded blacklist:

1. Ask users to add you

The best plan of attack to prevent being blacklisted is to ask customers to whitelist you. Having your customers add your sender address to their address book increases your deliverability since ISPs will see you as a personal contact of this individual customer. An added benefit is that this is a way to get your emails out of the Promotions tab and into the main inbox.

2. Don’t use link shorteners

Link shorteners from, Buffer and Tiny can be extremely useful in helping shorten long URLs (especially ones with tagging at the end), but can be detrimental in the eyes of an ISP. These shortened links mask the original URL leads, which is convenient for spammers in hiding the CTA of an email. While not all blacklists currently factor this into their algorithm, it’s safer to steer clear of these shortened links.

3. Manage unsubscribes

Regularly manage your contact list to ensure it’s up to date and that all unsubscribes and bounced emails are removed from the list. Sending to customers that have opted out not only damages their trust for you, but also affects your deliverability rates. You can work with your tech team to automate this process. Mailjet’s Event API is intended to be used this way.

4. Monitor blacklist status

Another important item to monitor regularly is your blacklist status and sender score. Once a week, use sites such as Return Path or to check your IP address against these databases and make sure that you aren’t blacklisted.

5. Read up on latest spam news

As spammers continue to fine tune their “craft”, ISPs refine their algorithm on a regular basis to combat this. Unfortunately we’re limited in our knowledge of what exact characteristics their tracking, but what we can do is to keep up to date on the latest deliverability trends, spam and security issues. Some deliverability blog we frequent are Magill Report and Return Path.

What other tips and tools do you use to stay off ISP blacklists? We’d love to discuss below.

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