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It sounds like you have a paper tray jam.. But it could be internal. So lets go to this page and start with the paper tray jam selection.
And it will walk you through the entire process of clearing the envelope. http://support.brother.com/g/b/faqlist.aspx?c=eu_ot&lang=en&prod=mfc7360n_all&ftype3=1969
If you cant get to the envelope following that step, try the internal jam option from that page. One of the options on that page will definitely help you find and remove the envelope. Its just a matter of where the envelope ended up before it got stuck~
If you encounter any issues or need further assistance, let me know.
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