Optimize Test-MtCisSharedMailboxSignIn.ps1

[ricmestre]

Description

This optimizes Test-MtCisSharedMailboxSignIn.ps1 with the following:

• Added EXOSharedMailbox command to Get-MtExo so that it retrieves only shared mailboxes with Get-EXOMailbox -RecipientTypeDetails 'SharedMailbox' instead of retrieving all mailboxes and filtering them locally
• Retrieve the users associated with the shared mailbox using Graph batches instead of individually
• Assign loop result to a variable instead of expanding an array on each pass

This PR also adds -ResultSize 'Unlimited' to both EXOMailbox and EXOSharedMailbox commands so that it actually retrieves all mailboxes instead of bumping into a limit so this also should fix an issue:

• Fixes 🪲 Get-MtExo not retrieving shared mailboxes #1417

Contribution Checklist

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[Copilot]

Pull request overview

This PR optimizes the Test-MtCisSharedMailboxSignIn function to improve performance and fix issue #1417 where shared mailboxes weren't being retrieved in large tenants. The optimization introduces a new EXOSharedMailbox command to Get-MtExo that retrieves only shared mailboxes directly from Exchange, adds -ResultSize 'Unlimited' to prevent pagination limits, and uses Graph API batching to retrieve user information efficiently instead of individual requests.

Changes:

• Added -ResultSize 'Unlimited' to EXOMailbox command in Get-MtExo to retrieve all mailboxes without pagination limits
• Added new EXOSharedMailbox command to Get-MtExo that filters for shared mailboxes at the Exchange level
• Replaced individual Graph API calls in a loop with batched Graph request using array of IDs for better performance

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
powershell/public/cisa/exchange/Get-MtExo.ps1	Added -ResultSize 'Unlimited' to EXOMailbox command and created new EXOSharedMailbox command for filtered retrieval
powershell/public/cis/Test-MtCisSharedMailboxSignIn.ps1	Updated to use new EXOSharedMailbox command and implemented Graph batching for user retrieval

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