Any specific setting in zone security settings you suggest I change on my end?
Budd78,
I wouldn't suggest, because as I mentioned I do not personally use Outlook.
Obviously it depends on what settings you have already set and also, as mentioned, what format your incoming mail takes. I can't recall, did you say 'some' mail gets through?.
You need to look through the settings and see if any applies to your situation. You could 'if you have an otherwise secure machine/installation', try putting all of the zones to the low settings and then run a few test mails. This should tell you if my 'guess' holds any water and if it proves anything you can then track down the particular setting.
Reset your security when you've finished.