Find all mailboxes where user mailbox have access to

Question

Hello guys !

I need to find all mailboxes where user mailbox have access to

I tried via Get-Mailbox | Get-MailboxPermission(...) also XPO but it is still loading and occurs i/o issues and others faults...reason why it does not works as expected is my tenant have huge number of users few thousands for each domain so the method taking a lot of time and occurs mentioned issues - not effective

My idea was get all mailboxes of user domain and after it execute mentioned query but, they do not know if user do not have access to mailboxes of different domain, so in this solution I should get list of users for each domain and after it check it one by one... - not effective

My question is if any solutions exists on that ? it not must to be in powershell maybe some audit? I need just list of objects where user have full access rights.

objects means shared mailboxes, room mailboxes, user mailboxes,
for groups it is completed through AAD.

Thanks for your time

Answer 1

@Tomasz Dyszy

You could try with the script below to check permission for shared mailboxes, room mailboxes, user mailboxes (There doesn't exist full access permission for distribution group):

$mailboxes = Get-Mailbox -ResultSize unlimited | where{$_.RecipientTypeDetails -ne "DiscoveryMailbox"}  
  
foreach ($mailbox in $mailboxes){  
    Get-MailboxPermission -Identity $mailbox.UserPrincipalName | where{$_.user -notlike "*self*"}  
}  

If it still takes a long time to run which caused failure, you could check permission based on domain:

$mailboxes = Get-Mailbox -ResultSize unlimited | where{$_.RecipientTypeDetails -ne "DiscoveryMailbox" -and $_.UserPrincipalName -like "*@domain.onmicrosoft.com"}  
  
foreach ($mailbox in $mailboxes){  
    Get-MailboxPermission -Identity $mailbox.UserPrincipalName | where{$_.user -notlike "*self*"}  
}  

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Answer 2

If you want this information for specific user, use the -User parameter. For example:

Get-Mailbox | Get-MailboxPermission -User vasil

Details here: https://www.michev.info/Blog/Post/1516/quickly-list-all-mailboxes-to-which-a-particular-user-has-access

If you want it for multiple users, or you have a big set of mailboxes to go over, best use a proper "inventory" type of script instead of oneliners.