Client rendering quirks: Outlook, Gmail and Apple Mail

Outlook for Windows

1. 1Uses Word to render: no flexbox, no CSS grid, no background images.
2. 2Adds spacing around images — we set display:block and border:0 to stop it.
3. 3Rounded corners on buttons fall back to square. That is expected.

Gmail

1. 1Strips <style> blocks, so everything must be inline.
2. 2Clips messages over 102KB — keep signatures small.
3. 3Rescales on mobile; avoid fixed widths above 600px.

Apple Mail

The most forgiving of the three, but it will override your font unless the user unticks “match my default message font” when creating the signature.