When scheduling a meeting users type in a users name and Outlook grabs a
cached address instead of the Exchange address. Thus, they are unable to see
the person’s availability and/or the invited person receives a plain email
instead of a true meeting request. For example assume a user foo having the
email address of , but also existing in the Exchange environment
as foo. If a user at some point sends an email to instead of
using the exchange address, the non-exchange address is cached by outlook.
Then at a later point when addressing a meeting request Outlook will present
two options for name completion 1) the email address and 2) the exchange
address. Most users do not know the difference between the two and will
select the completion... and then availability won't show up.