While adpiucf post is very great, it is long.
Basically, treat them with respect and dignity.
Remember, they were there before you were and if not for them, you may have not be there now.
Alums are there to help for The Love of the Sorority and The Chapter. they have been through all of the Newbie, Ritual, Officerships, Sisterhood, and Love.
They are not strangers, they are Sisters, older maybe but still Sisters. Act proffesional and give them a little thank you!
A little thank you is all that is asked.