Hello @DanRuby ,
This is a standard security setting on Outlook, and must be managed from either your network side, or the individual recipients' ends. I'd recommend checking out the following articles for info that will aid you and your IT in safelisting our domains:
Safelisting our domains
Safelisting email addresses
I'd also strongly advise setting up self-authentication for better delivery and to make Outlook trust the sending source better.
Ultimately, based on how Outlook generally functions, it may force images to require a manual download / approval to show regardless of the safelisting steps taken, since Outlook tends to be incredibly intense with its security algorithms.
See also:
Missing images overview
Display issues blog post
Displaying images in email programs
Clipped and collapsed content in Gmail/Outlook
... View more
