If you get a delivery error message when sending an email to internal contacts, it is sometimes due to the migration from the old to the new Exchange server.

The email address you entered could not be found. Check the recipient's email address and try sending the message again. If the problem persists, contact your email administrator.

Outlook offers an AutoComplete of the recipient by default when writing an email. Unfortunately, when importing the mailboxes, Outlook's AutoComplete list was also migrated from the old Exchange. This refers to the entries on the old Exchange server, which are no longer resolved correctly.

Only the complete deletion of this list helps:

• File > Options > Email
• Scroll to "Send messages"
• Click the "Clear AutoComplete list" button

Your own contacts remain. It is just the auto-complete list in Outlook.

Independently of emptying the list, you can pick out the "right" recipient from the global address book for each email.

• Variant (1): Click "To" and select the contact from the global address book.
• Variant (2): Enter the name and press "Ctrl + K". This will give you the corresponding contact suggestion from the global address book.