Update Set-MailUser.md

[Dean-Haas]

Added description per https://office.visualstudio.com/MAX/_workitems/edit/10026456

[learn-build-service-prod]

Learn Build status updates of commit f1ab0b8:

✅ Validation status: passed

File	Status	Preview URL	Details
exchange/exchange-ps/exchange/Set-MailUser.md	✅Succeeded	View (exchange-ps)

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[learn-build-service-prod]

Learn Build status updates of commit d79152e:

✅ Validation status: passed

File	Status	Preview URL	Details
exchange/exchange-ps/exchange/Set-MailUser.md	✅Succeeded	View (exchange-ps)

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[learn-build-service-prod]

Learn Build status updates of commit 04ed181:

✅ Validation status: passed

File	Status	Preview URL	Details
exchange/exchange-ps/exchange/Set-MailUser.md	✅Succeeded	View (exchange-ps)

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel