I have 5 penpals who happen to be male. We've been exchanging emails for several years and all but one has a girlfriend. I have never met my penpals, there has never been any sexual conversation or anything that could resemble flirting on either side. I have been open with partners that I have male friends who I am penpals with. I would be fine with letting them see the emails, but they've never asked. If someone is open and honest there shouldn't be a problem.