I'm not a service desk guy, but wouldn't it be better to have notifications being sent from a different account to the one being used to auto-log incidents? Hopefully you have that option available to you and then your notifications can have links to the appropriate pages and email addresses to use.
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Include the email account for the service desk email itself in the ones to ignore for a start, just in case!
I think you'd best be doing this at the server end with some rules on there. LDSD itself doesn't have this idea of a whitelist
How about removing the email service and giving them a set of request to click on just for then on the self service portal?