Removing Email Addresses from Outlook's AutoComplete Cache

Outlook maintains a "nickname" list that is used by both the automatic name-checking and the AutoCompletion features. The nickname list is automatically compiled as you address email messages. If the nickname cache becomes corrupt, Outlook may send to an incorrect or old email address,.

Outlook remembers up to 1000 email addresses you've used in the past, even if you have never stored them as Contacts. There are pros and cons to this behavior.

• The main benefit is that you can easily retrieve email addresses you have used in the past, just by typing the first few letters of the email address.
   
• A major drawback is that Outlook's AutoComplete entries are static and cannot be updated, which can easily lead to email bouncebacks if you are not careful. This means that, despite changing a contact's email address several times, Outlook will always suggest the first email address that was used.

Delete a single cached entry:

1. Open a New Email in Outlook. Start typing the address in the To field. When the suggestion list appears, hover over the unwanted entry. Click the X next to it to remove it.

Delete the entire Autocomplete List via Outlook Options

1. Open Outlook.
2. Go to File > Options > Mail.
3. Scroll to the Send messages section.
4. Click Empty Auto-Complete List.
5. Confirm by clicking Yes.