By default, Microsoft exchange uses the username when creating email addresses for users using Recipient Policy.
However, in many cases the standardised email address format is slightly different – for example:
This is actually really easy to edit in the Exchange System Manager using a few variables:
%g = Given Name (First name).
%3g = means first 3 letters of Given Name
%s = Surname (Last name).
%3s = means first 3 letters of sn.
%d = displayname.
%m = Exchange alias.
Once this has been edited, just right click on the Policy and click Update this Policy now.