In most cases, email that bounces from what appears to be a valid email address happens due to a corrupt cached entry. Address entries can occasionally become corrupted on the server and can propagate even after they are repaired.
A cached entry allows Exchange users to type part of a name, then have the rest autocomplete to known addresses. If a cached entry is corrupt (e.g., firstname.lastname@example.org) then that cached entry will be used EVEN IF the user types the entire address.
A corrupted entry may look like the following:
<IMCEAEX-_O%3DUNIVERSITY%2B20OF%2B20DELAWARE_OU%3DEXCHANGE% 2B20ADMINISTRATIVE%2B20GROUP%2B20%2B28F YDIBOHF23SPDLT%2B29_CN%3DRECIPIENTS_CN%3DMusername@win.udel.edu>
A corrupt entry can happen for a variety of reasons, which are fairly rare. However, the problem is that if a person tries to send mail to a corrupt entry (username, in the above example) and copies people on that message, the people who were sent a copy will also get the corrupt cached entry, which may replace a good entry in their cache--sort of like a virus.
So, if Joe has a bad entry for Mary, and he sends a note to Mary, Peter, and Paul, now Joe, Peter, and Paul will have corrupt entries for Mary, and the next time any one of them tries to send email to Mary that e-mail will bounce.
The fix is simple and is user-based because the corrupt entry is in the user’s account. The corrupt entry needs to be deleted. Two methods exist to delete entries: The user can delete ALL cached entries (not a good idea because the user will now have to rebuild his or her cache by typing full names) or the user can delete the single entry.
To delete a single cached entry, follow these steps:
Now, the next time you send email to this person, you can type most of the name and allow Outlook to resolve it from the server’s global address book.