For the user :recall will fail under certain conditions.
If you send a message by accident, you can attempt to recall the message from the recipients using Recall This Message on the Tools menu. The message recall feature allows you to recall, replace, or delete messages that you have sent.
Message Recall will not be successful if:
The recipient is not using Outlook.
The recipient is not logged on to the mail service provider.
The message has been moved from the Inbox.
The message has been read.This includes viewing the message with the Preview Pane so that the message is flagged as Read.
NOTE: The Message Recall feature is only available in the Corporate Workgroup option.
MORE INFORMATION
Torecall or replace a message, follow these steps:
On View menu, click Folder List.
On the Folder list, click Sent Items.
Open the message you want to recall or replace.
On the Actions menu, click Recall This Message.
Click to select, "Delete unread copies of this message", to recall the message. To replace the message, click to select "Delete unread copies and replace with a new message", click OK, and then type your new message and send it.
To receive notification about the success of the recall or replacement, click to select "Tell me if recall succeeds or fails for each recipient" check box.
Click OK.
For the boss, I doubt very much that he will be able to recall the message since the message was sent from the user mailbox (sent items, outlook just works that way, send as and sent on behalf sent the mail from the persons mailbox and not from the "other mailbox she has access to".)
Hope this clarify the issue.
