Send On Behalf permissions for another user means that another user can send mail on your behalf.
The other user (the delegate) will be able to choose your email address in the From field when sending a message.
IMPORTANT: both your address and your delegate’s address will appear to message recipients
To assign user to Send On Behalf another user:
1) Open WorldPosta control panel.
2) Click on Mailboxes in Hosted Organization section.
3) in Mailboxes page, click on the user that you want to edit.
4) Click on the tab Mail Flow Settings.
5) In the section Send On Behalf click on Add button, a contact list will appear.
6) Check all users you want to grant this permission to, then click Add Accounts.