Why does sender IP get blacklisted ?

Why does sender IP get blacklisted ?

A blacklist is a list of IP addresses and domain names that an organization has decided to block for spam, malware or a configuration that promotes bad email behavior. Even if your email systems are properly configured and running optimally, your clients, partners and prospects may reject your email because you are blacklisted.

There are a large number of reasons you could be blacklisted: last month’s malware attack, a marketing campaign was reported as spam, or an email server configuration that forwards spam are some common reasons. Regardless of how you might get on a blacklist, monitoring blacklists for your email servers and domains is a necessity.

Once you’ve stopped doing whatever put you on the blacklist and put in place safeguards to prevent further issues, you need to contact the blacklists. MxToolbox provides detailed information on each blacklist and links to the blacklist, including delisting resources.

Refer link for more details - http://mxtoolbox.com/blacklists.aspx