An email signature ships with every message you send — hundreds of copies a week. Getting the image wrong costs you either credibility (blurry logo) or goodwill (a 2 MB attachment on every reply).

The Dimensions

Think in display size, then export at double:

  • Logo: displayed 120–200 px wide (or 40–60 px tall for a horizontal lockup). Export at 2× — 240–400 px wide — and set the displayed width in the HTML/signature editor. This is what keeps it sharp on Retina and high-DPI screens.
  • Headshot: displayed ~80 px square, exported at 160 px.
  • Banner / promo strip: displayed 500–600 px wide max — that's the safe body width for email clients, including Outlook's narrower rendering. Export at 1000–1200 px.
  • Social icons: displayed 16–24 px, exported at 32–48 px; better yet, use text links to avoid a row of tiny images.

Never let a signature image exceed 600 px displayed width — beyond that it forces horizontal scrolling in some clients and gets scaled unpredictably on phones.

The Weight Budget

  • Keep each image under ~50 KB, and the whole signature under ~100 KB. Signatures are re-sent on every reply in a long thread, so the cost multiplies.
  • Compress to a target size rather than eyeballing quality. A 400 px logo at 30 KB is easily achievable.
  • Format: PNG for logos with transparency or sharp text; JPEG for photographs. Avoid animated GIFs — many corporate clients block or freeze them.

The Things That Actually Break

  • Blocked images. Most clients hide images until the reader clicks "show images". So never put essential information — name, title, phone — inside an image. Use live text for those and images only for branding. Always set descriptive alt text.
  • Dark mode. A logo on a hard white background shows as a glaring white box in dark themes. Use a transparent PNG whose artwork works on both light and dark, or accept a subtle rounded white card as a deliberate choice.
  • Hosted vs embedded. Linking to a hosted image keeps the email tiny but shows a broken icon if the URL ever moves and can be blocked as a tracking pixel; embedding travels reliably but adds weight to every send. Hosting on your own stable domain is the usual compromise.
  • Scaling in the client. Always declare explicit width/height so a 2× image is displayed at 1×; without it, some clients render the image at full pixel size and blow up your layout.

Quick Build Order

Crop the logo tight → resize to 2× the intended display width → compress to under 50 KB → set the display width explicitly → send yourself a test and read it on a phone, in dark mode, with images off. If it still communicates with images blocked, the signature is done right.