Hi @Safs-3080
Agree with michev. Send As Allows the delegate to send messages as if they came directly from the mailbox or group. There's no indication that the message was sent by the delegate.
You could refer to the official document to assign permission for userA
In Exchange online: Manage permissions for recipients in Exchange Online
Add-MailboxPermission -Identity "sharedmailbox" -User userA -AccessRights FullAccess -InheritanceType All
In on-prem Exchange: Manage permissions for recipients
Add-ADPermission -Identity "sharedmaibox" -User userA -ExtendedRights "Send As"
If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.