The Auto-Complete List is a feature that displays suggestions for names and e-mail addresses as you begin to type them. These suggestions are possible matches from a list of names and e-mail addresses from the e-mail messages that you have sent over time. When you first start to use outlook, you will not have any contacts in your Auto-Complete List, but this will fill up over time.
By default, this feature is turned on in Outlook. If you type a "b" in one of the recipient fields in a new message, for example, the list presents suggested matches and shows all names in your list with a first name, last name, or email address that begin with "b." The list is refined with each additional character you type.
In the
Outlook client, if you are entering a recipients name for
the first time who appears in the global address list for Parkland, you
can select the
Check Names option in the ribbon prior to entering
in their entire name. This will bring up a list of possible
suggestions from that address book. The more characters you enter prior
to selecting Check Names, the more refined the results will be. Select
the correct recipient from the list and click
OK. That person's
name/address will be auto-filled into the To field. Once that message is
sent, that person will be added to your auto complete list. If you are
not seeing the recipient, it is possible that the person is not in the
global address list or you are misspelling the name.

In
Outlook on the web,
if you are entering a recipients name for the first time who appears in
the global address list for Parkland, there is no Check Names option,
however, as you type a popup will appear listing suggestions based on
the characters that you have entered. If you are not seeing the correct
name, you can enter additional characters or select the
Search Directory option at the bottom of the list. Select the correct recipient from the list and click
OK. That
person's name/address will be auto-filled into the To field. Once that
message is sent, that person will be added to your auto complete list.
If you are not seeing the recipient, it is possible that the person is
not in the global address list or you are misspelling the name.

For the most current up to date information, including editing your auto-complete list, please check out the following help article from Microsoft:
https://support.office.com/en-us/article/Manage-suggested-recipients-in-the-To-Cc-and-Bcc-boxes-with-Auto-Complete-dbe46e31-c098-4881-8cf7-66b037bce23e