Can you please provide us with more information. What happens when the user with the phone deletes the e-mail from the phone?
Generally when sending from hotmail its not something that loops meaning it doesn't keep happening over and over again... It should send the message once to recipient. Then said recipient receives said e-mail on phone. I have seen rare cases with corp accounts where mail was stuck in a nastay forward loop. However this is far and few between.
Try deleting the message on phone, then have user pull the battery from phone and try again to ensure mail is not acting up.
Let us know if that doesn't work and we will bring some more ideas to the table.