It looks like my company server, which I believe is Exchange / Office 365, is stripping HTML in signatures when sent by any Mac client, including Outlook 2011 for Mac. All HTML is removed and links are simply exposed bare.

For example, "<a href="http://microsoft.com">My link</a>" will become "My link<http://microsoft.com>". All <img> tags are removed, all <table> tags etc.

I reproduced this with both Outlook 2011 for Mac and Apple Mail 8.1 (OS X 10.10.1 "Yosemite"). This does not happen when using Outlook for Windows. In both cases, I connect to the server through Exchange Web Services.

Has anyone else seen this? I suspect it might be a server-side "security feature" triggered by all non-Windows clients, but it's really annoying and surely there is an option to stop it from happening...?