Spamhaus DBL is a realtime block list focusing on domain name, your deliverability will be dramatically impact once your domain listed by DBL. Some website will stop their user from jumping to your domain, like twitter.
And unfortunately, shortly after successfully setting up my own mail server, I was listed in the Spamhaus DBL. Due to my limited knowledge of Spamhaus and maintaining a well reputaion, it took many different attempts before I finally identified the cause and successfully had my domain delisted through customer support. I must say Spamhaus’s customer support was very friendly and responded promptly.
I tested the deliverability of emails sent to Gmail and Outlook through mailreach.co. During 2-3 tests, I sent approximately 100 emails, and most of them were marked as SPAM. This number of SPAM emails is relatively small for Gmail and other major email service providers. Even though I was listed in the DBL, I could still send emails to Gmail. However, since Outlook uses DBL data, I could not send emails to Outlook.
From Spamhaus’s perspective, a newly established domain that quickly sets up a mail server with a very high SPAM rate led to my SMTP score dropping to -4, with a total score of -7, resulting in immediate inclusion in the DBL. But actually gmail has a SMTP score of -3🤷♂️. Based on my observations, the threshold of SMTP scores for being listed in the DBL is around -4.
Before confirming that the test was the cause, I also tried the following: sending bulk emails to my Gmail account while ensuring they were not marked as SPAM, approximately 300 emails per day. By monitoring the data, I found that emails marked as SPAM by Gmail affected my score immediately, while emails not marked as SPAM will affected the score in a possitive way. During the days of heavy email sending, my SMTP score did increase, leading me to realize that it might be related to the very high SPAM.
After customer support agreed to delist my domain, the score was immediately reset to 0, but all previously recorded data of listing will not be deleted.
