Sending out unsolicited emails(product promotion) can get your website on a blacklist as a webmaster, especially if you're sending to thousands of people. Chances are that one or more of the recipients of your mail can mark it as SPAM and the email service provider of that recipient might place your website on a blacklist if it's reported too often. 

Another likely scenario is that if you observe that your regular website traffic has reduced considerably, one of the likely reasons could be that your website has been blacklisted. This is why it is very important for you to always check if a domain name is blacklisted or not before buying.

There are several organizations that operate and oversee the blacklist service on the internet. Most email service providers run checks to see if a website is blacklisted with DNSBL or SURBL. They make use of these services to try to eliminate spam mail before it reaches the user. Some DNSBL service providers use a variety of criteria to list and delist website addresses.

Most Spam filters used by email service providers use DNSBL services as the first line of defense. SURBL is not the first line of defense in checking spam mail, however, It contains a directory of websites that have been blacklisted for appearing in the text of spam emails. Both these methods are used by email service providers as protection against spam mail.