Outlook has a function that causes it to remember email addresses where they have been successfully sent. This is called "Autocomplete”, similar to how your Google remembers previous web addresses and pre-populates the address bar.
Autocomplete data is stored as a file on your computer, and occasionally an autocomplete entry can become corrupted, and this requires deletion of that autocomplete entry.
To delete a single entry from autocomplete:
- If you are in the middle of composing an email, copy the text to Notepad or other application.
- Start typing the email address that you are unable to send an email to:
- You will observe an cross or “X” adjacent to the address.
- Click on the X to delete the entry.
- Manually type the email address again and send your email when ready.