What are your boundaries for opposite-sex friends?

Or same-sex, if you go that way.

A friend recently commented, “I can’t believe [some guy’s] wife lets him have female friends.”

I also read this in an advice column question today: “I’ve tried to explain my belief that a man should not be ‘buddies’ with another man’s wife, but my wife doesn’t see it and says they’re just pals.”

These seem like pretty extreme positions. My partner and I are freaks with boundaries at the opposite extreme.

So I am wondering: How do you navigate this kind of friendship in your relationship? What would constitue emotional infidelity to you? What are your boundaries, and how do you resolve conflicts about this kind of issue?