In the battle against spam, ISP’s came up with strong spamfilters. Due to this spam filtering process some legitimate emails were also blocked, known as false positives. To avoid this kind of email deliverability problems, a process of whitelisting was implemented, certainly not the easiest method. Why would an ISP whitelist a sender if it isn’t of any interest for him? But anyway, whitelisting procedures are almost over. The new standard is Reputation Management.
The reputation of your sender IP address is increasingly becoming the main factor that determines whether or not your email will end up getting blocked by the spam filter. And relevance plays a huge role in it.
The reputation scoring mechanism looks at several factors of your email communication. This list of factors will probably grow as ISP’s are trying out more mechanisms that are based on the interaction with your e-mails.