I had a lot of problems with evolution since I installed CentOS 6. The corporate mail server is MS Exchange. I am on my own. Many many times I would start evolution, enter the password for the Exchange Server, be prompted again and again for the password. Once in a while evolution would actually connect to the MS Exchange Server and I would see my mail. I think that I may have found the problem. You see evolution wants to store the password in the "Passwords and Encryption Keys". It really does. In order to do this the item "Passwords: keyring" must be set as the default. I set it to the default and then started evolution. It works!