This is going to be a little esoteric, but if you are one of the 6 people in the world who do this sort of thing, you will be interested.

We made an outlook plugin for Marketo.  It will pull HTML Email templates out of Marketo, so you can send them from Outlook.  The first interesting thing is that Outlook, when it sees HTML that has a direct reference to an image like:

<img src="http://www.site.com/images/foo.gif">

Outlook will not respect this tag.  It will actually EMBED the graphic into the page and change the markup to something like:

<p class="msoNormal"><img src="cid:23490234"></p>

They wrap a <P> tag around the image, for no reason as far as I can tell.  Interestingly (or not) this is a real mess.  The reason is that the class msoNormal is defined as having no margins/padding.

Of course, Gmail, strips out all classes from their email client, which means.

Outlook -> Gmail messages will inherently mess up any embedded image by putting a normal <P> around it.  Bye Bye rounded corners!

For all you web developers out there who say, “Oh it’s so hard to deal with the 10 browsers out there”…you don’t know the hell that is email development.  Boo email industry!  Boo!