You can add save a contact's Email Address to the Bio of their Contact Profile.
If Email Messaging is turned on for your organisation, you can use the email address of each contact to:
Send them emails
Receive emails from them
Steps
Go to the Contact Profile page of the contact whom you want to add the email address of
Press either of the Edit Bio buttons
You arrive on the Edit Contact buttonpage
Scroll down to the field that has been designated as an Email Address field.
If it is in a different Contact form tab, select that tab and scroll down until you see the designated Email Address field. (Read step-by-step instructions on how to edit a contact’s bio)
Enter the email address in the field
Press save