smtp wont relay messages for hotmail

I have built a site where users can send out messages to other users with similar interests, this is done with smtp on iis6, soon to be iis7. WHat Im finding though is that every now an then messages dont get through to SOME users with hotmail 开发者_JS百科accounts. Is this something I can sort via iis?

thanks

Check the undelivered mail folder on your SMTP Server. IF the hotmail messages are there then hotmail is refusing delivery from your mail server.

The undelivered aka bounced email folder may also contain delivery notifications if your admin mail forwarding is not setup properly. These will provide more direct information as to the cause of failure.

If both of these fail, setup a script to send a message to a hotmail account and then retrieve it. When the test message fails to be retrieved, the script can then capture DNS resolver cache and other useful info to give you a hint as to what went wrong.