I was pulling my hair out on Wednesday trying to figure out why certain inline images in an email I was generating would not display in Outlook, whereas others would.
What's more irritating is that all of the images worked in Outlook Web Access; only the desktop client of Outlook wouldn't display some of the images.
The problem is that something like this is really hard to troubleshoot. After going down many different paths--such as assuming that I was attaching the image incorrectly, or perhaps that Outlook didn't like spaces in its inline attachments, and so on--I finally found the solution.
Outlook was recently patched to flag image references that have a src attribute with a capitalized CID. Thus, changing < img src = "CID:myimage" > to < img src = "cid:myimage" > fixed the matter.
Oh man. That’s frustrating. So I’m blogging about it in hopes that I might save someone who googled the issue like I did from wasting a couple hours of time.
