September 15, 2020

Create shared mailbox & delegate rights.

New-Mailbox –Name "John, Doe" -Shared -PrimarySmtpAddress ***shared-mailbox-email***
Add-MailboxPermission "John, Doe" -User userUPN -AccessRights FullAccess –InheritanceType all
Add-RecipientPermission "John, Doe" -Trustee userUPN -AccessRights SendAs -confirm:$False
set-mailbox -Identity "John, Doe" -GrantSendOnBehalfTo @{Add="userUPN"}