Domain Blacklists are databases that identify domains known to deliver spam or harmful content in real-time. ISPs (Internet Service Providers) define them, and email servers use them as references to decide whether an incoming email may be trusted.
Due to a history of undesirable activity, email domains that are blacklisted are likely to be classified as spam.
Your domain could be placed on a blacklist if:
Your emails have low engagement (open rate, response rate, etc.)
A substantial percentage of your sent emails are marked as spam by recipients.
You send emails with a high bounce rate.
You send emails to "Spam Traps" (inactive email addresses that are used to spot spam behaviour).
Your domain has been hacked, and spammers are using it against your will.
Your domain is less likely to be blacklisted if you use good sending practices and active authentication methods like SPF, DKIM, and DMARC.
How to get delisted
Most ISPs and ESPs (Email Service Providers) filter emails based on blacklist records; therefore, having your domain banned will severely impact your deliverability.
If this occurs, you have two options:
Wait. The majority of blacklists will eventually delete your domain from their database. Depending on the infraction's severity, the process's duration can vary but is often between one and three weeks.
Ask for removal. Some blacklists provide removal or delisting request forms. Provide context, demonstrate that you are not a spammer, and inquire why you were blacklisted, so you don't make the same mistake twice.
On the website of the blacklist provider itself, you will discover additional information regarding the delisting procedure.