I would agree with this:

I do have a few male friends, mostly casual, one close. With my closer friendship we've always had to be aware of boundaries especially as I'm happily married and want to stay that way. There are certain things (such as my marriage or his relationships or sex) I won't ever discuss with my male friend and he respects that. It's required much more thought than same gender friendship, but I agree it's nice to have a man's perspective, and I do think men and women can successfully be friends in many cases.

I also agree about all conversations between friends being open to your partner - and meeting each other is essential. Everything, texts, emails have to be open and visible.

From my experience I would also recommend telling your partner why you would not consider your friend a potential romantic partner even if you were single. This helped reassure my husband hugely, and it also helped clarify things in my mind. A note of caution here, if you would consider your friend as a potential partner if you were single then it's not a good idea to maintain a friendship.