I previously posted how to backup the auto-complete list in Outlook by using the NickName file.  I ran into a much more common problem today where old entries in the nickname file are no longer valid and caused me to send messages to the wrong people or old addresses.  I did a quick Google search and came up with a few helpful bits of information.  The first of which is a handy utility that will let you modify the contents of the nickname file and in my case remove the old address.

1. NirSoft’s NK2View – Freeware http://www.nirsoft.net/utils/outlook_nk2_autocomplete.html.  They also have a lot of other handy little utilities for Outlook management and other systems.
2. When adding new addresses the best way to do it is actually create a contact entry in the PST file, but as many people know contact email addresses do not always appear in the drop down list.  Still best practice says to add a new contact.
3. ALWAYS backup the nickname file (read Part 1) because if the file gets corrupted your out of luck!

Good Luck!

-Brent