Mail Connection issues to aol with yosemite 10.10.1
You are not alone.  I have the same problem using earthlink as email provider.  Answer is that you use "MacMail" on your computer which connects to your provider.  The connection is broken in the yosemite system.  Earthlink support has tried to remotely check and reset internal macmail settings in my computer, with no success.  Call your provider, maybe the can reset some hidden setting in yosemite.  Good luck.