Email Signature Size, Images and Hosting: An IT Guide to Signatures That Render Everywhere (2026)

TL;DR: Keep the whole signature within about 600 pixels wide and roughly 100 to 200 pixels tall without a banner. Use PNG for logos and icons, JPEG for photos and GIF only for one animated element; avoid SVG and WebP, which some major clients convert or don't show. Host images on a domain you control or your signature vendor's CDN and reference them by URL; don't embed them as base64 data, which Gmail doesn't display. Upload images at about twice their display size and always set width and height in pixels, so they stay sharp on high-density screens and don't blow up in Outlook. Design logos to survive dark mode, use web-safe fonts, and allow-list your image domains wherever a proxy, firewall or CRM content policy sits between the image and the reader.

Last reviewed: October 2026.

Most broken signatures aren't a design problem; they're a rendering problem. The same HTML is displayed by Gmail, classic Outlook (which uses Word to render), the new Outlook, Apple Mail and a dozen mobile apps, each with different image handling, CSS support and privacy features. This guide gives IT and brand teams the numbers and the reasoning: recommended dimensions, how hosted, attached and base64 images behave, which formats work, why signatures look blurry or huge, dark mode, fonts, and which domains to allow-list. Client support data below comes from Can I email, an open, test-based reference for email client support; check its pages for the date each feature was last tested.

What size should an email signature and its images be?

There's no standard; these are our working recommendations for company signatures, with the reasoning, plus Google's published guidance where it exists.

Element	Display size (CSS pixels)	Upload at	Why
Whole signature	Up to about 600 wide; about 100–200 tall without a banner	n/a	Fits a desktop reading pane and a phone without horizontal scrolling
Logo	About 120–200 wide, up to 60–80 tall	2x	Readable without dominating the message
Headshot	About 70–100 square	2x	Matches Gmail's 70–100 px recommended image height
Social and contact icons	About 16–24 square	2x	Large enough to tap, small enough to keep the line tidy
Banner	About 400–600 wide, 80–150 tall	2x	Same width as the signature; short enough not to read as an ad

Google's own guidance for Gmail is a signature image "70–100 pixels high by 300–400 pixels wide", with a maximum of "100 pixels high by 1000 pixels wide" (Gmail Help: troubleshoot signatures). That's guidance for a single image in Gmail's own editor; banners deployed by a signature tool are commonly taller, so test them in Gmail.

File size matters for load time more than for layout. Scribe accepts JPEG, PNG and GIF uploads up to 5 MB and resizes them to fit the signature, but recommends GIFs "under 2MB" to avoid slow loading on mobile (Scribe: image library, Scribe: GIFs). For static logos and headshots, aim for tens of kilobytes, not hundreds.

Should signature images be hosted, attached or embedded as base64?

There are three ways to get an image into a signature, and they behave very differently.

	Hosted (linked by URL)	Attached inline (CID)	Base64 data URI
How it works	<img src="https://…">; the client downloads the image when the message is opened	The image travels as a MIME part and the HTML references cid:	The image is encoded inside the HTML as data:image/…
Message size	Small; only the URL is in the message	Adds the image file to every message	Adds about a third more than the file to the HTML
Shows without "load images"	No; depends on the recipient's image settings	Usually yes	Where supported, yes
Gmail	Yes	Varies; some clients also list inline images as attachments	Not supported in Gmail on web, iOS or Android, per Can I email
Classic Outlook for Windows	Yes, after images are allowed	Yes	Partial: Can I email reports base64 GIFs don't render
Can be updated after sending	Yes, by replacing the file at the same URL	No	No
Click and view tracking	Possible	No	No
Gmail's 10,000-character signature limit	Only the URL counts	n/a	Encoded data counts and quickly exceeds it

Source for the base64 rows: Can I email: base64 images. For company signatures, hosted images are the practical default: they keep messages light, work in Gmail, fit Gmail's signature limit (see the "signature too long" guide) and can be swapped centrally. Their weakness is that they depend on the recipient loading remote images, which is why every image needs meaningful alt text and the signature must still make sense without them. Microsoft's own sample for Outlook mobile signature add-ins uses an inline attachment for its icon (Microsoft Learn), so you will meet CID images in vendor tools too.

What recipients' clients do with hosted images

• Gmail scans images before showing them and lets users choose "Ask before displaying external images" (Gmail Help: images). It serves images through Google's proxy servers, which is why images that depend on internal IPs or cookies break; Workspace admins can exempt trusted internal URLs with an image URL proxy allowlist (Google Workspace Admin Help).
• Classic Outlook "is configured by default to block automatic picture downloads from the Internet"; users or admins can relax it per sender or in the Trust Center (Microsoft Support).
• Outlook for iOS and Android, when managed with Intune, defaults to loading images only for internal senders and Safe Senders (Microsoft Learn).
• Apple Mail with Mail Privacy Protection downloads remote content privately in the background when a message arrives, hiding the reader's IP address and whether they opened it (Apple Support). Images display, but open tracking from signature images is unreliable for these readers.

Which image formats work in email signatures?

Format	Use for	Support notes
PNG	Logos, icons, anything with flat color or transparency	Supported across Gmail, Outlook and Apple Mail (Can I email)
JPEG	Headshots and photographic banners	Universally supported
GIF	One animated banner or logo at most	Classic Outlook may show only the first frame; with a Microsoft 365 account, Can I email reports the animation plays three times, then stops (Can I email: GIF). Scribe notes that clients without animation show the first frame (Scribe), so put the key message in frame one
SVG	Avoid	Gmail renders SVG images but rasterizes them to PNG, and inline <svg> isn't supported in Gmail or Outlook (image SVG, inline SVG)
WebP	Avoid	Not supported in classic Outlook for Windows; Gmail converts it to JPEG (Can I email: WebP)

Scribe's uploader accepts JPEG, PNG and GIF only, which matches this list (Scribe: image library).

Why do signatures look blurry, broken or huge?

• Blurry: the image was uploaded at display size. Phones and most laptops have high-density screens with two or three device pixels per CSS pixel. An image uploaded at exactly 150 pixels wide and displayed at 150 looks soft. Upload at twice the display size and set the display size with width and height.
• Huge: no explicit dimensions. If the HTML doesn't set width and height attributes, some clients show the image at its full file size, so a 2x headshot appears twice as large. Always set both, in pixels. Scribe's image blocks set width and height in pixels for this reason (Scribe: image blocks).
• Huge in classic Outlook: DPI scaling. Classic Outlook composes and renders with Word. Microsoft documents that images can grow larger for recipients after a user changes Windows to a higher DPI setting, a behavior introduced with Word 2010 (Microsoft Learn). That article covers attached graphics; email developers report related scaling of body images on high-DPI displays. Pixel-based width and height attributes and images saved at 96 DPI reduce the effect; the new Outlook is built on the Outlook web client rather than on Word, so it renders like Outlook on the web.
• Square corners in classic Outlook. Classic Outlook for Windows ignores CSS border-radius (Can I email), so a round headshot made with CSS shows as a square. For a guaranteed circle, crop the image to a circle on a transparent or solid background before uploading.
• Background images missing. Classic Outlook doesn't support CSS background images, and Gmail strips styles containing some url() backgrounds (Can I email). Put text on a solid color, not on an image.
• Broken image icon. The URL moved, the host needs a login or internal network, a proxy or firewall blocked the domain, or the Drive file isn't shared publicly. Google notes Drive images must be public to work in a Gmail signature, and work accounts may need an admin to allow it (Gmail troubleshooting article above).
• Images missing only in the sender's Apple Mail. Scribe documents a known Apple Mail bug where the sender's own signature images don't display while composing, even after turning off Protect Mail Activity; recipients still see them (Scribe: images not showing).

How do you design signature images for dark mode?

Dark mode is applied by the recipient's client, and clients do it differently: some leave the message alone, some invert light backgrounds, some invert everything. Support for the CSS that would let a sender control it, @media (prefers-color-scheme), is limited: Apple Mail supports it, while Gmail and classic Outlook for Windows don't (Can I email). Scribe takes the same view and doesn't offer dark-mode image variants because "there is currently no reliable technical way to provide a separate dark mode version of an image that all email clients will respect" (Scribe: image library). What works:

• Don't use a dark logo on a transparent background. On an inverted or dark background it disappears. Use a version with a solid background, or add a thin light outline or glow around the mark.
• Prefer mid-tone brand colors for text and icons; pure black text and pure white backgrounds are the elements most likely to be inverted.
• Check both modes before deployment. Scribe's preview has a light and dark toggle for every teammate's signature (Scribe: preview). Then confirm on a real phone in dark mode.

Which fonts render everywhere?

Web fonts mostly don't work in email. Can I email reports that @font-face isn't supported in Gmail or in Outlook for Mac, web, iOS and Android, and that classic Outlook for Windows ignores remote fonts (Can I email). When a client can't load a font it substitutes a system font, so a signature designed in a brand typeface can look different for every recipient. Use a web-safe stack. Scribe limits signatures to 11 web-safe fonts for this reason: Helvetica, Arial, Arial Black, Arial Narrow, Tahoma, Georgia, Times, Garamond, Verdana, Lucida and Trebuchet (Scribe: fonts). Never put a name or phone number inside an image to get the brand font: it's invisible when images are blocked, unreadable to screen readers and can't be copied. For a design-led comparison of typefaces, see Scribe's post on the best fonts for email signatures.

Which image domains need allow-listing?

Hosted images fail silently when something between the image host and the reader blocks it. Check these:

• CRM and sales tools with a content security policy. Salesforce blocks images from domains that aren't trusted. Scribe's Salesforce setup asks the admin to add *.sendassets.io and *.sigassets.com under Security > Trusted URLs with the img-src CSP directive (Scribe: Salesforce). Other web-based sending tools with a CSP need the same treatment.
• Web proxies and secure email gateways. If your proxy or gateway rewrites or blocks external image URLs, add your signature image domains so internal recipients see logos.
• Gmail's image proxy. Images hosted on internal addresses or behind cookies break in Gmail because of the proxy; host signature images publicly instead, or use the Workspace image URL proxy allowlist only for trusted internal domains, as Google advises.
• Outlook Safe Senders. For internal mail, adding your own domain to Safe Senders, or using the Intune default for Outlook mobile, lets colleagues see signature images automatically.
• Server-side DKIM. If signatures are added in transit, configure the vendor's DKIM record. Scribe's Google Workspace server-side guide says DKIM keeps mail out of spam and avoids "missing assets such as images and links" (Scribe: Google Workspace server side).

How much does a signature add to every email?

A hosted-image signature adds only its HTML to each message, typically a few kilobytes, so it doesn't affect attachment limits or mailbox storage in any meaningful way. Attached (CID) images add their full file size to every message and every reply, which adds up in long threads and in archives. Base64 images add their encoded size to the HTML and are the reason many signatures break Gmail's 10,000-character signature limit. Two practical rules: keep a template's HTML under about 8,000 characters so individual data fits under Gmail's limit, and, on Microsoft 365 or a server-side install, use a lighter on-reply variant without banners so threads stay short (Scribe: variants).

Where does Scribe fit?

Scribe's editor produces inline-styled, table-based HTML designed for Gmail, Outlook and Apple Mail, with images stored by Scribe and linked from the signature (Scribe: compatibility). The shared image library takes JPEG, PNG and GIF up to 5 MB, resizes them, and has auto-crop and background removal; image blocks set pixel width and height and an optional corner radius (image library, image blocks). Fonts are limited to web-safe choices, and the preview shows every teammate's signature in light and dark mode before you install it. Banner campaigns can be scheduled by department and revert automatically when they end (Scribe: campaigns). The same signature is deployed through the Microsoft 365 add-in, the Google Workspace app, Salesforce and server-side routing. Pricing is per user, with a free plan for up to two users and a 14-day trial (pricing).

Frequently asked questions

What is the best size for an email signature?

Keep the whole signature within about 600 pixels wide and roughly 100 to 200 pixels tall without a banner. Google recommends Gmail signature images 70 to 100 pixels high and 300 to 400 pixels wide, with a maximum of 100 by 1,000 pixels.

What size should a logo be in an email signature?

Display it at about 120 to 200 pixels wide and no more than 60 to 80 pixels tall, upload it at twice that size for sharpness on high-density screens, and set width and height in pixels in the HTML. Use PNG, and avoid a dark logo on a transparent background because it disappears in dark mode.

Should email signature images be embedded or hosted?

Hosted, for company signatures. Linked images keep messages light, work in Gmail, fit Gmail's 10,000-character signature limit and can be updated centrally. Base64 images aren't displayed by Gmail, and attached CID images add their file size to every message and reply.

Why is my email signature image blurry?

It was probably uploaded at exactly its display size. High-density screens need about twice as many pixels. Upload the image at 2x and set the display width and height in pixels.

Why do signature images look huge in Outlook?

Usually because the HTML doesn't set width and height, so Outlook shows the file at full size, or because classic Outlook, which renders with Word, scales images on high-DPI Windows settings. Set pixel dimensions on every image and save images at 96 DPI.

Can I use SVG or WebP images in an email signature?

Avoid both. Can I email reports that Gmail rasterizes SVG images to PNG and doesn't support inline SVG, classic Outlook for Windows doesn't support WebP, and Gmail converts WebP to JPEG. Use PNG for logos and icons, JPEG for photos and GIF for one animated element.

How do I make an email signature work in dark mode?

You can't control dark mode reliably, because Gmail and classic Outlook ignore prefers-color-scheme. Use a logo with a solid background or a light outline, mid-tone brand colors, and preview the signature on a dark background before deploying it.

Which domains should IT allow-list for signature images?

The domains your signature images are served from. For Scribe, the Salesforce setup lists *.sendassets.io and *.sigassets.com as trusted URLs with the img-src directive. Also check web proxies and email gateways, and configure the vendor's DKIM record if signatures are added server-side.

Related Handbook guides

• Gmail "signature too long": cause and fix
• Company email signatures on mobile
• Signatures in the new Outlook, Outlook on the web and Outlook mobile
• Email signature banner campaigns
• Client-side vs server-side email signatures