I moved this from Business to Home > SecurityCenter as I think that is the product you are using.
Open SecurityCenter and go to Web and Email Protection > Firewall > Network Connections for Programs
Click the word Program at the top to re-arrange alphabetically (takes a while to load)
Locate your email client and all of your browsers, in particular IE even if you never use it (McAfee does), and make sure that all have Full access using the Edit button if necessary to change that.
I assume that you've already checked the browser and email settings themselves to make sure images aren't blocked?
The other factor that could be involved is, did you install Family Protection or Parental Controls?
Thank you!! I went right to where you instructed and changed "Net Guard" to <off> for Microsoft Outlook
and the images [after reboot] showed up on the next email!!
There you go, all is well now, good ;-)