At Exclaimer, we see a lot of email signatures. We see what a lot of companies get right and what they get wrong.
DO keep it slim
Very wide signatures will not render well in Outlook’s Preview Pane before you open an email or the window after you double-click it.
The industry standard is about 650 pixels, but we’d suggest making a signature thinner (600px) to ensure nothing gets lopped off the edge.