I am creating Transport Rules to create company-wide signatures. One of the quirks that I noticed was that, while everything looks great for HTML mail, anything sent in plain-text includes a bit of ugly HTML code (eg. [a href] tags, etc).

I tried getting around that with a condition that Message Header "Content-Type" includes "multipart".

Unfortunately, that doesn't work. I believe it fails because all HTML emails include two Content-Type headers. The first for HTML, and the second for fall-back to plain-text. Exchange seems to only count the final "Content-Type" header... which is always "plain-text".

So.. does anyone know how to apply a Transport Rule only to HTML emails, without requiring a third-party product?



Not directly an answer to your question but as an older question already couldn't solve the opposite - detecting text content - it just seem's that the transport rules are too limited.

Looking at your goal, you might be able to use disclaimers (which it seems that these are internally realised with some more powerful (programatic) transport rules).

The disclaimer text is the text that's inserted into a message. Exchange 2010 inserts disclaimers into e-mail messages by using the same message format as the original message. For example, if a message is created in HTML, the disclaimer is added in HTML. If the message is created as plain text, HTML tags are stripped from the disclaimer text before it's added to the plain text message.

  • Daniel, thanks.. Yes, I'd seen the older post. But it addresses Exchange 2010, and much changed with 2013. Unfortunately, disclaimers will suffer the same issue: much of what is in HTML will be mangled if the message is sent in plain text. Examples include IMG and A HREF tags. For new emails, it shouldn't be a problem... but often enough our employees reply to plain-text mail, and reply in the same format as the originating email... meaning, plain-text. – ltwally Mar 4 '16 at 19:27

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