After installing Yosemite I can send but not receive email on my Mac

My service provider went through all my preferences and said it is an Apple issue. We checked the correct port settings etc. I have gone through the Apple help page and re-entered all the information, saved and retried. Connection doctor still has the same message that connection to this IMAP has failed and to verify my username and password. I have done this twice with my service provider and twice again using the Apple help site and it is not helping.