Custom mapping of open directory users first name.lastname@domain not short name@domain that is no standard in any way
Maybe change option how to connect to OD ( not kerb) , in my OD setup i can connect with the email address i provided on user creation to other setups like own cloud.
even if you can only connect to it only that way you can read first name ,last name from directory and use that as email adress creation.
shortname@domain is really not ANY standard first name.lastname is.
adding 300 aliases per hand then telling users to SET their aliases is unprofessional.