Below powershell can help to apply users full access rights and and SendAs permission to the mailbox for the given input CSV file

Format ofthe CSV something like this

UserMailbox,User
Krishna,Domain/Krishna

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$csv = Import-csv -path “C:\Userdetails.csv”
foreach($line in $csv)
{
Add-MailboxPermission $Line.UserMailbox -AccessRights FullAccess -user $Line.User
Add-ADPermission $Line.UserMailbox -Extendedrights “Send As” -User $Line.User

}

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