Just a quick note in case anybody else is foolish enough to try add MS gradient filter to a button...

I thought I'd do this for the benefit of Outlook users...

I added the following CSS declaration to the inline styles on a CTA button:
filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#23d329', endColorstr='#039b0a',GradientType=0 );

What happened:

  • Gradient declaration was only interpreted by the 2010 version of Outlook.
  • This and all other CSS declarations are stripped out in Outlook.com web. Everything - including a fallback background color - gone. (As there's a inner span around the link text to stop it getting coloured I ended up with white text on a white page. Not good.)

Conclusion.
Don't use MS filters. Horrible things.