Convert a 'text' email address field to 'Email' format

Hi - 

Is there a 'ToEmail' function of some form?  I have a list of email addresses, but it's the Key field from a sync'd table (not editable) and it's 'text' format.  I want to create a formula email field where it looks at the key field and converts it to a more usable 'email' format. 

Is this possible?

Thanks folks!!