One possibility. . . .
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answers.microsoft.com/en ··· ies#tabsIf not. . . . a few questions that pop to mind . . . that may help pinpoint the cause. . . .
what format (ie. html richtext textonly) is the sender's email client?
Is the body text still contained within the original outgoing email? (copy should reside in the sender's sent folder)
what format is the recipient email set for. If it is set for text only. . . is there any chance that they have a message.txt file also attached?
does viewing the message source on the recipient's end show any signs of the original body text?
Do you have access to the email server? If so. . .is the body still there when it hits the server?
Could this be some outlook "quirk" like the (always wonderful) winmail.dat crapola?