Hi @Laurent
Welcome to our forum!
How do you import contacts to Outlook client?
If you add a contact directly from the Outlook client, will it show up in the To field?
According to my tests, populating the To field is also related to Outlook's autocomplete feature. Please check that you have enabled autocomplete. Go to the File >Options>Mail>Use Auto-Complete List to suggest names when typing in the To, Cc, and Bcc lines.
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