Depends on your version, which you did not post.
No full versions of Outlook ever had the ability to add recipients
automatically to your Contacts Folder. Only the long abandoned IMO mode of
Outlook 98/2000 did that. To automatically add the email address of people
you respond to to your Contacts Folder requires code:
http://www.outlookcode.com/d/code/autoaddrecip.htm
http://www.slipstick.com/contacts/addauto.htm

Signature
Russ Valentine
[MVP-Outlook]
Hi Russ
Saw your post to Jaz and I was looking for an answer to a problem I have had
for a while - your answer has me more puzzled.
I am using Outlook 2002 SP3 (10.6515.6735) on XP Home
Somehow my copy stores email addresses that I have replied to - I cannot
remember when it started and as you say I can find no switch for this in
Outlook (or Plaxo which I have as an add-in).
The problem is it does not add them to the Contacts address book so I have
been unable to delete unwanted addresses, as a result when I type a name into
To: or CC: I get all the email addresses for a person up to 4 sometimes of
which 3 are out of date. This has caused some trouble when a contact has
changed companies - it is easy to accidently pick the wrong one especially as
they may all show as 'John Smith' but actually relate to different addresses.
Any suggestions?
Thanks
> Depends on your version, which you did not post.
> No full versions of Outlook ever had the ability to add recipients
[quoted text clipped - 5 lines]
> > How do I set Outlook to auto save the email address of the person I'm
> > replying to so that it automatically saves into my contact list?
Brian Tillman - 04 Jan 2006 16:27 GMT
> The problem is it does not add them to the Contacts address book so I
> have been unable to delete unwanted addresses, as a result when I
[quoted text clipped - 3 lines]
> accidently pick the wrong one especially as they may all show as
> 'John Smith' but actually relate to different addresses.
This sounds like autocompletion. When you start to type an address, the
autocompletion feature will display a list of all addresses starting
similarly and to which you've previously sent mail. Delete the unwanted
ones by using the down arrow to select one you don't want and pressing
Delete.

Signature
Brian Tillman