If using Cached Mode or Personal Folders, Outlook discovers a recall request when checking the server mailbox for new messages. Outlook doesn't just process a recall request as soon as it reaches the recipient mailbox. Outlook will try to satisfy the request as soon as it discovers that a request was received.'

In How Exchange Message Recalling Works, I hinted this point when saying: 'At some point the recipient's MS Outlook client processes this recall request. So Exchange applies a conversion that renders the request readable to any SMTP email client, but in doing so it loses all the functionality. These cannot be easily sent out over the internet. Instead, Exchange specific Rich Text Messages are used. Outlook recall requests are not based on a standard internet protocol. Recalling emails sent to recipients outside your Exchange Organization will not work. Today we conclude this discussion exposing less known recall failure conditions and other interesting nuggets. We also went through the most common recall failure reasons. Here we saw that all functionality is implemented at the MS Outlook client. We started discussing the internals of native Exchange message recalling in How Exchange Message Recalling Works.

How to recall a message in outlook 2011