Just turn off autocompletion. Outlook will then use autoresolution to search
your Contacts for an match to what you type in the To: field. You can force
autoresolution at any time with Ctrl-K.
Here's a primer:
Autoresolution resolves the name you are typing in the address field of a
new message (To, CC, or BCC) by searching through your Contacts Folders to
provide you with the correct e-mail address. This feature is enabled by
checking the box for "Automatic Name checking" in Tools > Preferences >
Email options > Advanced Email options. To use this feature, follow these
steps:
Open a new message window. In the address field, type the first three
letters of a name or an e-mail address that is stored in one of your contact
records (only one letter is needed if using Outlook 2003). Invoke
autoresolution by clicking out of the address field (tabbing out of the
field will also invoke autoresolution in versions prior to 2002, but not in
versions 2002 and higher). You can also use the "Check Name" toolbar button
(the one that has a red check mark and a picture of a person) or press
CTRL+K. Note that if you tab out of the address field in later versions
(Outlook 2002 or 2003) you will no longer invoke autoresolution because
those versions also have the autocompletion feature running. In those
versions you will be selecting whatever entry is highlighted in the
autocompletion suggested names dropdown.
Once you invoke autoresolution, your Contacts Folders will be searched. If
you have more than one Contact matching the name you have typed (in either
the First Name, Last Name or email fields), the name you've typed will
acquire a red wavy line below it and you will be prompted with a list of
potential matches found so you can designate which address to assign to that
name.
Autocompletion is a feature that is new in Outlook 2002 and above. As you
begin to type a name in an address field of a new message, Outlook offers to
complete the entry based on aliases or names from e-mail messages that you
have previously sent. Note that this feature starts functioning immediately
after you have typed the first three letters in the address field (or only
one letter in Outlook 2003) and does not require that you Tab out of the
field or hit CTRL+K. Also note that it does not use your Contacts Folder as
its data source but rather a cache of information Outlook stores in the NK2
file that is created from the email addresses in messages you send. At
first, the feature may appear not to be working since it takes a while for
Outlook to populate its cache. The autocompletion feature is enabled by
default when you install Outlook 2002 or 2003, but you can disable it by
clicking "Options" on the "Tools" menu, clicking "E-mail Options" on the
"Preferences" tab, and then clicking "Advanced E-mail Options," then uncheck
"Suggest names while completing."
In Outlook 2002 and above, both autoresolution and autocompletion features
exist. Since both features can be in play, it is easy to get confused as to
whether you are using autocompletion or autoresolution. Just remember that
autocompletion is in play as soon as you have typed 3 or more letters (or
just 1 letter in Outlook 2003 and 2007) in the address field and remains in
play until you click out of the field or expressly invoke autoresolution by
one of the methods listed above. As long as one of the names suggested by
the autocompletion feature remains highlighted in the address field
dropdown, tabbing out of the field will select that name as the sending
address. Clicking out of the field will not, and then autoresolution will
come into play. Also, if autocompletion finds no matches in its cache (and
therefore suggests no names), then autocompletion is no longer in play and
autoresolution will take over once you tab out of the field. In Outlook
2003, you can also invoke autoresolution at any time by hitting "Escape"
while typing in the address field. Once autocompletion is no longer in play,
then Outlook will try to resolve the name you enter against your various
Contacts Folders, but not against the autocompletion cache. .