I have one large image (599x249px, 75Kb) at the start of my email, and when I test in Outlook 2003/2007/2010/2013 the image is missing. In most of them it’s just a normal “missing image” icon, but in 2010 it actually says “The linked image cannot be displayed. The file may have been moved renamed or deleted. Verify that the link points to the correct file and location”.
But the image is there, can be accessed by its URL, shows up in all other clients etc. It’s not CMYK. All the other images are fine.
Is this a known issue with the first image in Outlook, or with images over a certain size? Do the EmailOnAcid email clients need their caches cleared, as suggested by this note from CampaignMonitor:
Is the header image or logo missing in Outlook and Outlook isn’t giving you an option to download? We’ve seen that happen and rebooting our computer cleared Outlook’s cache. After rebooting, we were able to see the seemingly broken image.