Update mail-api-overview.md with a clarification on Outlook client behavior

[relawler]

Important

Required for API changes: this is not an API change

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Add other supporting information, such as a description of the PR changes:

This update adds in two sentences to the Outlook mail REST API overview to clarify that if a message is updated via API, Outlook clients will not refresh the view and a user will need to reopen the mail to see any update

Based on customer request for clarification in documentation.

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[learn-build-service-prod]

Learn Build status updates of commit 129e892:

✅ Validation status: passed

File	Status	Preview URL	Details
api-reference/v1.0/resources/mail-api-overview.md	✅Succeeded

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