Dynamics CRM has been around for a while (about 13 years) and, as is the way with any software, there are a few design features from the old days which linger today. One of those is how email addresses are treated for Accounts, Contacts, and Leads.
How Emails Work in CRM
Basically, for an Account, Contact, or Lead you have three email addresses: emailaddress1, emailaddress2, and emailaddress3. All three are used for linking Activities to records but you can only...
Continued on Source: Wrestling With Email Address Limitations – That CRM Blog