Give Send As permission to a user

Send As permission is used when you need to give a user permission to use another recipient’s email address in the From address. In order to give Send As permission to a user on Office 365 you need to use Windows PowerShell.

To give Send As permission to a user use these cmdlets:

1.Connect Windows PowerShell on your PC to the Office 365 service:

$LiveCred = Get-Credential
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri -Credential $LiveCred -Authentication Basic -AllowRedirection
Import-PSSession $Session

2.Grant a user permission to access another user’s mailbox:
Add-MailboxPermission <mailbox> -User <user or security group> -AccessRights FullAccess

3.Give Send As permission to users:
Add-RecipientPermission <identity> -AccessRights SendAs -Trustee <user>