exchange server 2003 7004 errors

We get a bunch of 7004 and 7010 errors and I am trying to figure out how to remedy this. For some reason we get messages that say user needs to authenticate first so the e-mail doesn't get delivered. I believe this may have something to do with IIS but am not positive nor do I know how to fix it. Any others going through this that may have some answers, please reply. Thanks you.