Problem Description
- Outlook says: The email address you entered couldn't be found. Please check the recipient's email address and try to resend the message
- You have double checked that the email address is legitimate and there are no spelling errors
- Using Outlook web access or another webmail solution works fine to send an email to that address
Problem Resolution
This occurs because Outlook has cached the wrong email address or a corrupt version of the email address in the previous recipients / autocomplete list.
See Microsoft's guide on clearing either that record or all records from the autocomplete list: https://learn.microsoft.com/en-us/outlook/troubleshoot/contacts/information-about-the-outlook-autocomplete-list#how-to-clear-the-whole-autocomplete-list
