How do I configure contacts to use just first or nickname in email addresses?

When I send emails to contacts, the TO line contains the full name.  How do I configure my contacts so only the first name appears with the email address in the TO address without losing the full name in my contacts.

The way i do it is create two contacts for each person. 1 with only a Nick name in the First Name contact field and the 2nd contact with the real First & Last Name in separate fields as normal.

There is also an option in the EMClient Contact / Details Tab to put in a Nick Name.