Powershell command to check Send-As Permissions

Find all users who have Full Access to the mailbox of others:

Get-Mailbox -ResultSize Unlimited | Get-MailboxPermission | ? {($_.AccessRights -match "FullAccess") -and 
not ($_.User -like "NT AUTHORITYSELF")} | ft Identity, User

Finding all users who have Send-As :

Get-Mailbox -Resultsize Unlimited | Get-ADPermission | ? {($_.ExtendedRights -like "*send-as*") -and -not
($_.User -like "nt authorityself")} | ft Identity, User -auto

Finding all users who have Send-As (Restricted to an OU):

Get-Mailbox -Resultsize Unlimited | Get-ADPermission | ? {($_.ExtendedRights -like "*send-as*") -and
($_.Identity -like "*/SomeOU/Users/*") -and -not ($_.User -like "nt authorityself")} | ft Identity, User -auto

Find out who a particular user can Send-As:

Get-Mailbox -Resultsize Unlimited | Get-ADPermission | ? {($_.ExtendedRights -like "*send-as*") -and -not
($_.User -like "nt authorityself") -and ($_.User -like "DOMAINUsernameUwantToFind")} | ft Identity, User -auto