@JustinMicheal-7973
1) The -SourceMailboxes in Set-MailboxSearch command doesn't support the "add" action:
You need to set the value directly: Set-MailboxSearch holdName -SourceMailboxes user1,user2,user3,user4
Here is a example for parameter which supported ”add“ action: -EmailAddresses
2) There doesn't exist limitation about it, you could contain all mailboxes in one hold.
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