Take a look at this link and see if it helps
I've been using Windows Live Mail, but I'm with Comcast. I had to change my port to 587 though, and never had a problem. Try clicking APPLY before clicking OK and see if that helps. Occasionally WLM can get quirky and you have to uninstall and reinstall it although I haven't had to do that for at least a year. If you do that, but sure to save your contacts and any email you don't want to lose first.

Good luck.