Send As and Send On Behalf

One of the more common requests that Exchange adminsitrators get it to allow an assistant to be able to send email as another person. 

Source:  http://support.microsoft.com/?kbid=327000

 

Grant "Send on behalf" permissions

If you grant a user "Send on behalf" permissions for another user's mailbox, that user can send mail on behalf of the mailbox owner. The name in the From box of these messages appears as

where DelegateUser is the name of the user to whom you granted "Send on behalf" permissions and where MailboxOwner is the name of the user who owns the mailbox.

To grant a user "Send on behalf" permissions for another user's mailbox:

1.	Click Start, point to Programs, point to Administrative Tools, and then click Active Directory Users and Computers.
2.	In the console tree, click Users.
3.	In the right pane, right-click the mailbox of MailboxOwner, and then click Properties.
4.	Click the Exchange General tab, and then click Delivery Options.
5.	Under Send on behalf, click Add.
6.	Type the name of the DelegateUser, click Check Names to verify the name, and then click OK.
7.	Click OK, and then click OK.
8.	Quit Active Directory Users and Computers.

For example, if you grant UserB "Send on behalf" permissions for UserA's mailbox, UserB can send messages on behalf of UserA. The From box in these messages appears as follows:

Grant "Send as" permissions

If you grant a user "Send as" permissions for another user's mailbox, the DelegateUser can send mail as the MailboxOwner. The From box in these messages appears as follows:

To grant a user "Send as" permissions for another user's mailbox:

1.	On an Exchange computer, click Start, point to Programs, point to Microsoft Exchange, and then click Active Directory Users and Computers.
2.	On the View menu, click to select Advanced Features.
3.	Expand Users, right-click the MailboxOwner object where you want to grant the permission, and then click Properties.
4.	Click the Security tab, and then click Advanced.
5.	In the Access Control Settings for MailboxOwner dialog box, click Add.
6.	In the Select User, Computer, or Group dialog box, click the user account or the group that you want to grant "Send as" permissions to, and then click OK.
7.	In the Permission Entry for MailboxOwner dialog box, click This Object Only in the Apply onto list.
8.	In the Permissions list, locate Send As, and then click to select the Allow check box.
9.	Click OK three times to close the dialog boxes.

For example, if you grant UserB "Send as" permissions for UserA's mailbox, UserB can send messages that appear to be sent from UserA. The From box in these messages appears as follows: