How do you disable Server OS X in Mountain Lion?

I read the article provided by apple on how to disable the OS X server in Lion found at http://support.apple.com/kb/HT4827.

I did as instructed, but in step 6, there is no "Dedicate system resources to server services" option.

The problem I am having is related to the mail program. It is a common problem, but none of the fixes are working for my computer. I can receive mail fine, but when I go to send mail it says that "An error occurred while trying to sign this message with a certificate from “myusername@gmail.com”. Verify that your certificate for this address is correct, and that its private key is in your keychain." I have it set up to where my password is the auth. for the account.

I am new to mac and most of the jargon is over my head. If anyone can provide new info on how to uninstall the server and fix my mail, I would be extremely happy!