Having problems with internet connectivity. Have checked settings and they seem correct as best I can tell.

Have been trying to trouble shoot for hours the problems I'm having with Apple Mail. I'm sure there is one tiny box some where that doesn't have the correct info.

I can connect to me.com, but not to gmail or comcast. All passwords are correct. I can connect to both servers on line, but not through Apple Mail... which is my preference. I keep getting that window pop up that requests the smpt server wanting my correct gmail password, but it gets refused. I've even made sure all email passwords are correct in my keychain. If it gets any more complex, then it's over my head. I need help.