From my review of outlook it appears that the auto email address prompt  does
not source all variables from the contacts / address book based on the
various components first name / last name / email address / nickname etc...

All email software I have previously used has dynamically prompted with
proposed complete email addresses when I may start typing the first name or
last name or even the email etc... Outlook appears to only allow
identification if you type the initial characters of the email address. Often
I do not recall obscure email addresses but can recall the surname of
firstname and would like to see a suggestion of possible matches from emails
in the contact list.