Graymail is a word used to describe "unwanted" email from a company or website. At some point a user would have agreed to receive the email via subscription list opt-in, but now considers the messages to be unwanted.
The word "gray" is used because the email falls between the "black and white" area of email spam and legitimate welcome email. Some recipients might consider this type of email spam (unwanted email) while others find the email useful (wanted email).
Examples of graymail include newsletters that you sign-up for (and often forget about but receive for years), messages you receive when you sign up for an online service or the automatic notifications received from online services, including social networking sites.
In October 2011, Microsoft announced a number of n initiatives for Hotmail, an online email service, to help users of its email service deal with graymail. Most graymail comes from opt-in/out services but it can be difficult to unsubscribe from some services, so in Hotmail you can now click on "unsubscribe," and it will notify the site to stop mailing you.