How to troubleshoot new account email issues?

Any tips on how I would go about troubleshooting email problems on multisite?

I often find the problem in spam filters or spamassassin filtering out the sites admin emails if not white listed.

I have a site that has been working fine but in the process of changing the admin address I screwed something up & now don’t receive any emails when a new account is created.

When the fill out the new site registration page all works and the account is created. However the usual emails are not sent to the user or site admin?

I have it on a dedicated server with cpanel.

Where I have all my other sites hosted my hosting company/server guy can always figure out email problems for me and usually point me in the right direction. The client that owns this is using godaddy for hosting and the support guys there are usually not much help at all.

I know I see threads where its recommended to start de-activating plugins one by one. Don’t think I have had many email issues in the past with WP but just curious if there are another useful email related tips ??

thanks!
-George