Email Address Searches
Although the below sites tend to return only very limited information with free accounts, most are reasonably cheap to have full access, allowing the searching of email addresses and mobile numbers, returning details and links to online accounts used with the email address or mobile number searched. These details can include names, screen names and profile images, which can then be searched to look for more information.
Anonymous, Disposable & Temporary Emails
Encrypted Emails
An interesting article about how to encrypt email, available Here