Outdated Address Information or Email Address is no longer valid

There are two possible solutions, clear all AutoComplete information or only the entries that are causing problems.

• Note:  clearing all AutoComplete information will mean that you will no longer see the suggested addresses when you start typing. Once you have emailed someone once, they will begin appearing as suggestions again. Clearing all AutoComplete information does not delete contacts from your address book.
• Recommendation:  clear all AutoComplete information because this will be more likely to resolve the problem permanently UNLESS you rely on the AutoComplete suggestions to find email addresses. If this is the case, it is recommended that you try removing the problematic entries one at a time first.
• If you find yourself needing to follow these instructions multiple times a year on the same machine, or if clearing all AutoComplete information does not resolve the errors, additional troubleshooting may be needed.

Method 1: Remove individual AutoComplete entries

1. In a new email message, begin to type the email address that failed until the AutoComplete box pops up as shown below
2. Click on the “X” next to the entry. If there are multiple entries for the same person, click the “X” next to all of them.

On older versions of Outlook, the “X” looks like this:

Repeat for each recipient that you have received error messages for.
 
Method 2: Remove all AutoComplete entries
 
Warning: this will remove all AutoComplete entries and no suggestions will be made until you rebuild your AutoComplete history; each person you email in the future will be added to the list

1. In Outlook, select File > Options > Mail
2. Under Send messages, choose “Empty AutoComplete List"
3. Choose Yes to confirm you want to empty the list.