What is an email blacklist? How to protect against spam email

Email black­lists help protect users from unwanted content like spam. Internet providers and external services often use ar­ti­fi­cial in­tel­li­gence to detect recurring, sus­pi­cious or fraud­u­lent patterns, placing those senders on a blacklist.

What is a blacklist?

‘Email black­list­ing’ refers to identi­fy­ing and blocking senders of spam so they can’t deliver messages. These senders are auto­mat­ic­ally added to a spam blacklist, which includes email addresses, domain names or IP addresses. Messages from black­lis­ted senders are auto­mat­ic­ally blocked from reaching accounts that use this list. Email black­lists are updated in real time. The opposite of black­list­ing is whitel­ist­ing. Another effective method of combating spam is greylist­ing.

How does black­list­ing work?

Black­list­ing works like a sieve: what’s un­desir­able (spam) is filtered out, while le­git­im­ate emails pass through. Black­lists use various criteria to identify and block unwanted content, including an email sender’s IP address, domain name, or even sus­pi­cious programs and file types.

Close

Despite their use­ful­ness, black­lists have lim­it­a­tions. For example, they can only block content that’s already known to be harmful, meaning threats are not blocked until the blacklist is updated. Unlike automated spam detection tech­niques), black­lists require manual upkeep by ad­min­is­trat­ors.

Which black­lists matter most?

Most black­lists are main­tained by the email providers them­selves, but there are also public providers often referred to as ‘spam police.’ These or­gan­isa­tions maintain spam filters and black­lists, send no­ti­fic­a­tions when a sender address is listed, or auto­mat­ic­ally block affected emails.

Key email black­lists include:

How do you end up on a blacklist?

Spam filters use scoring systems to evaluate incoming emails. Each provider has its own threshold for adding senders to an email blacklist. Common reasons for being listed include:

• Sending emails to inactive re­cip­i­ents or those who have pre­vi­ously marked messages from the sender’s address as spam. Returned emails (bounces) are also a red flag.
• A sudden increase in email volume, often triggered by seasonal pro­mo­tions, like summer sales, holidays or Black Friday campaigns.
• A rapid rise in sending frequency without notice. A high number of spam com­plaints almost always guar­an­tees a sender being placed on a blacklist.
• Using sus­pi­ciously large mailing lists – which can indicate a purchased list. Reputable lists grow gradually, not overnight.
• Tampering with email headers, es­pe­cially the ‘From’ and ‘Return-Path’ lines to create fake sender iden­tit­ies.

How can you avoid being black­lis­ted? 8 tips

Follow these best practices to reduce the risk of being listed on an email blacklist. Mass email senders, like news­let­ter services, need to be es­pe­cially careful.

1. Create varied content, so you don’t look like a spam bot. Avoid re­peatedly using the same phrases.

2. Obtain explicit consent from re­cip­i­ents before sending messages.

3. Use secure servers from certified providers and pro­fes­sion­al email marketing software.

4. Avoid personal or private email addresses. Use your company or brand name instead. Terms like ‘shop,’ ‘news­let­ter,’ or ‘contact’ work better than in­di­vidu­al names.

5. Get added to al­lowl­ists by asking re­cip­i­ents to ‘Save our contact in your address book’ or similar.

6. Avoid sending emails made up entirely of images, which many spam filters flag as having no content.

7. Do not use phrases that create ar­ti­fi­cial urgency, such as ‘Only three days left – book now!,’ or offer financial in­cent­ives that seem sus­pi­cious.

8. Avoid using ALL CAPS, or multiple ex­clam­a­tion points. Otherwise, you’re likely to end up on an email blacklist. Avoid topics such as gambling or certain med­ic­a­tion as these are often flagged by spam filters.

What to do if you’re on an email blacklist

Being listed on an email blacklist is not permanent. There are numerous lists, and appearing on one isn’t unusual – it may just indicate that your email marketing needs some fine-tuning. A few blacklist entries for your domain won’t sig­ni­fic­antly affect your email traffic. However, if your domain shows up on several black­lists, immediate action is required. When you find your domain or IP address on a blacklist, most providers offer in­struc­tions or links for re­quest­ing removal from the list.

How to create your own email blacklist using IONOS as an example

If you own a domain, many providers let you create and manage your own blacklist of unwanted senders. These emails are auto­mat­ic­ally re­dir­ec­ted to the spam folder.

With IONOS, you can set up your own email blacklist like this:

1. Log in to IONOS Webmail using your cre­den­tials.

2. Click the cog icon in the top right corner, and select All Settings to open the settings menu.

3. In the left-hand menu, go to the Anti-SPAM section.

4. Scroll down to the Personal Lists section and enter the email addresses you want to block under Blocked Senders.

Close