Update Set-TransportRule.md

[kellybos]

Need clarification for the message type condition. Encryption refers to S/MIME and Permission controlled refers to OME, rights management and sensitivity labels with encryption. Based on the wording of the value for this condition customers can be confused about expected behavior.

Thanks!

[opbld32]

Docs Build status updates of commit 165fe70:

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[opbld30]

Docs Build status updates of commit 0da7612:

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[opbld32]

Docs Build status updates of commit a58faa4:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
exchange/exchange-ps/exchange/Set-TransportRule.md	:white_check_mark:Succeeded	View (exchange-ps)

For more details, please refer to the build report.

Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

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[chrisda]

Closing as I made corrections in another redundant PR.