Hi Wayne,
Do you see a similar behavior if we try sending to the same email address in OWA?
Is the email address resolvable in the To/Cc/Bcc field? We mat try to manually type the full email address in the To, Cc or Bcc field, and then press Ctrl + K to resolve the email address.
Besides, is there any other users affected by this issue? You may also try testing on another computer to see the result.
Regards,
Steve Fan
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