4 billion email addresses

There are 3.6 billion email accounts in 2013, and by 2016, the number will reach 4.3 billion according to Campaigner.com (@CampaignerEmail).

Given that there are about 7 billion people on the planet according to the US Census Bureau, there is still room for growth. World email market share is about 50% by that measure. Email penetration in the US is higher at about 66% according to eMarketer.

MMS has email addresses for over 70% of US physicians, which is pretty consistent with the statistics above, indicating that physicians as one might expect are somewhat more likely than the general population.

One may expect that US email penetration will eventually approach 100% both in the general population as well as among physicians and other healthcare providers. Which is perhaps one reason why email is experiencing something of a renaissance. Another factor is the mobilization of computing. Email becomes perhaps the best way to reach people wherever they are--at home, at work, or on the go, as they are always able to check email regardless of location.

Another factor is the ability to use email as sort of a unique ID using something called "hashing". Hashing uses an algorithm to convert emails into 32-character hexadecimal strings which can then be used like cookies to segment and target customer lists without exchanging active email addresses. Learn more about that here.       

All and all, the future looks bright for email marketing.