Dissapearing Document

I think this is a user issue or a potential problem related to how the document is handled but I wanted to check with other MIS people. I have a user who routinely emails an excel spreadsheet back and fourth between them and a vendor and the form keeps vanishing off their network drive. I thought it may be a corruption so I had them build a new document but the same problem started again. Could this be related to them emailing it or does anyone else have an idea’s on what may be occuring with this spreadsheet?