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You can only recall messages when you use a Microsoft exchange email server; this is mostly for corporate/company email servers. If you use a general email provider, such as hotmail, yahoo, gmail, aol, etc., or if you use your Internet service provider's email, you cannot recall messages.

More details:

http://office.microsoft.com/en-us/outlook-help/recall-or-replace-an-email-message-that-you-sent-HA001230419.aspx

Unfortunately, once you have sent an email message, it is instantly sent to the other person's email Inbox, so there is no way to recall it. It is similar to the way that once your postal mail is picked up by the post office, you cannot stop its delivery. Per privacy policy, the email provider is not allowed to get into the other person's email Inbox and look through or delete his/her emails. When sending any email message, make sure to check carefully both the name and email address of any recipient as some names and addresses are similar.

Please let me know if you have any further question. Thank you.