Thank you for providing that info, and I apologize for missing the earlier bit about you testing beforehand. After speaking with the higher level technical team, it seems this is an issue that can sporadically happen with Outlook 2013, however data they've collected have shown that this can be sometimes resolved by tweaking O13's display settings.
Change the following setting: View tab > Reading Pane > Options.
Uncheck "Turn on automatic full-screen reading in portrait orientation"
Restart Outlook and send a new test email
If that doesn't help, you can also try:
File > Options > Mail > Message Format:
Reduce message size by removing format information not necessary to display the message
If that doesn't work, the only other workaround that they can suggest is to include a view as a webpage link for those who are not seeing the proper look of the email.
See also:
Display Issues blog post
Images Not Displaying in an Email Client
... View more
