Hi @Steve Gooch
To make sure I fully understand your situation, may I kindly check one detail with you?
Are you able to sign in and access the mailbox through Outlook on the web?
If the mailbox is accessible there, please try the following steps, as they often help resolve this type of situation in Classic Outlook:
- You may want to clear any stored credentials related to the affected account in Credential Manager > Windows Credentials.
I hope this information is helpful and provides some clarity.
Please feel free to share an update with me after trying the steps above.
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