Email Signature Images Not Showing? Here’s Why + How to Fix It

Cause 1: Images blocked by recipient’s email client (and why there’s nothing you can do about it)

I want to lead with this one because it’s the most common cause, and it saves you a lot of troubleshooting time to know when the problem isn’t actually your fault.

By default, Outlook blocks images in emails from external senders. The recipient sees your text and layout but gets a placeholder where images should be, along with the message “Right-click here to download pictures. To help protect your privacy, Outlook prevented automatic download of this picture.”

This is a deliberate privacy and security feature. External images can be used to track when an email is opened (via pixel tracking), so email clients block them by default for external senders. You cannot override this setting on your recipient’s behalf.

What you can do instead

• Add descriptive alt text to every image. The alt attribute renders as text when the image is blocked. alt="Acme Corp Logo" is infinitely better than a blank space or a broken image icon.
• Design the text-only version of your signature to still work.Your name, title, phone number, and links should all be fully functional even when images are hidden. Test this by disabling image loading in your own Outlook: File → Options → Trust Center → Trust Center Settings → Automatic Download → check “Don’t download pictures automatically.”
• Build trust over time.Outlook automatically allows images from contacts in the recipient’s Safe Senders list. If you email someone regularly, they may eventually be asked to allow your images, at which point they’ll see everything correctly.

For everything about designing signatures that work with and without images, see the email signature with logo guide.

Cause 2: Base64 encoded images showing as attachments in Outlook

This one is fixable and completely your signature’s fault — in a good way, because it means you can solve it. If recipients are getting your logo or photo as a file attachment (showing in the attachments bar or as a downloadable file), and the image isn’t displaying inline, you almost certainly have base64-encoded images in your signature HTML.

Base64 encoding embeds the image data directly in the HTML as a long string of text. It looks like this:

Gmail and most modern email clients handle base64 images fine. Outlook does not. Outlook treats base64 images as embedded attachments, strips them from the inline position, and shows them as files. The recipient sees an attachment called “image001.png” and wonders what it is.

The fix: switch to hosted URLs

Upload your logo and any photos to a web server — your company website, an S3 bucket, Cloudflare Images, or any publicly accessible host. Then reference the image with a normal URL:

Two important details in that example: always set both width and height as HTML attributes (not just in CSS), and always include alt text. Outlook ignores CSS dimensions but respects HTML attributes.

NeatStamp Pro hosts your images for you — you never have to worry about where to put the file or whether the URL will stay alive. On the free plan, use any stable public URL. The Outlook signature setup guide explains exactly how to paste your final signature HTML into Outlook correctly.

Cause 3: Image URL is broken or expired

This is the sneakiest cause because everything worked fine when you set up your signature, and then months later images start breaking. If your signature was working and has suddenly stopped, this is the first thing to check.

Copy the image URL from your signature HTML and open it directly in a browser. You should see the image. If you get a 404, a blank page, or a generic hosting error, the image is gone and needs to be re-uploaded.

Common reasons URLs break

• Website redesign: Your company relaunched the website and the image folder was reorganized. The old URL /images/logo.png now lives at /assets/brand/logo.png.
• Hosting migration:The company moved to a new web host and assets weren’t fully migrated or paths changed.
• Temporary image host used: Someone used a free image hosting service (like Imgur) that deletes images after inactivity or after a certain period.
• File accidentally deleted:Someone cleaned up “old” files on the server and removed what they thought was unused.
• HTTPS migration without redirect:The site moved from HTTP to HTTPS but the old HTTP image URL in the signature doesn’t redirect — it just 404s.

The solution in all cases: find the correct current URL for your image (or re-upload it to a reliable host), update your signature HTML with the new URL, and test again. To avoid this problem in the future, host signature images in a dedicated folder that won’t be touched during redesigns, or use NeatStamp’s image hosting which keeps URLs permanently stable.

Cause 4: Image file too large — spam filters and size limits

Large images in email signatures cause two separate problems: they trigger spam filters (which may strip or quarantine the message), and they make the email download very slowly on mobile connections, causing images to load slowly or not at all before the recipient moves on.

General size guidelines for email signature images:

How to reduce image file size without losing quality

• For PNGs (logos, graphics): Use squoosh.app or tinypng.com. TinyPNG typically reduces PNG file size by 50–80% with no visible quality loss.
• For JPGs (photos): Export at 75–80% quality. Most photo editors (even macOS Preview) let you set JPEG quality on save. At 80%, a photo that was 300KB typically drops to 40–60KB.
• Resize before exporting:If your logo is displayed at 150×50px, there’s no need for the file to be 1200×400px. Resize it to 300×100px (2x for retina) before uploading.

The email signature size guide covers the total size limits for the full email, not just images, which is worth understanding if you have multiple images in your signature.

Cause 5: Wrong DPI — why your logo looks blurry in Outlook

This one doesn’t stop images from loading — it makes them look bad. If your logo appears blurry or pixelated in Outlook desktop specifically (but looks fine in Gmail or web clients), DPI is often the cause.

Classic Outlook on Windows renders images at 96 DPI. If you export your logo at 72 DPI (the standard web DPI) at a display size of 200px wide, Outlook will render it at a slightly different size than intended, and the interpolation causes visible blur.

The retina fix for all clients

The cleanest solution is to export your image at 2x the display size and explicitly set the HTML dimensions to the display size. For example, if you want your logo to appear at 200×60px:

The actual file is 400×120px. The browser and email client scale it down to 200×60px for display. This renders crisply on retina screens (which is most modern displays) and looks fine on non-retina too.

For Outlook Web App and new Outlook (which behave more like browsers), this 2x approach is the right one to use. Classic Outlook desktop may still look slightly different, but the 2x technique is the closest thing to a universal fix.

For step-by-step Outlook image setup, see the Outlook signature guide. The email signature with logo guide has exact export settings for different design tools.

Cause 6: Gmail’s image proxy — why your logo URL changes

If you inspect the source of an email you’ve sent to a Gmail recipient, you’ll notice something: the image URL in the email has been rewritten to something like https://ci3.googleusercontent.com/proxy/.... This is Gmail’s image proxy, and it’s not a problem — it’s how Gmail works.

When a Gmail user opens your email, Gmail fetches your image from your server, caches it on Google’s infrastructure, and serves it to the user from Google’s servers instead. The user sees the exact same image — but it comes from googleusercontent.com, not your URL. This is why Gmail shows a single gray check mark for “delivered” rather than a blue tick when an email is read through proxy.

Why this matters for your signature

The Gmail proxy has two implications:

• Your image URL must be publicly accessible.Gmail’s servers fetch your image from your URL. If the URL requires authentication, is behind a VPN, or returns a 404, Gmail can’t cache it and the image won’t display.
• Caching means changes may not appear immediately.If you update your logo at the same URL, Gmail’s cache may serve the old version for a period of time. To force the new image, use a new filename (e.g., logo-v2.png) rather than overwriting the old file.

If your image shows correctly for Gmail users but not for Outlook users, scroll back up to causes 1 and 2 — this is usually image blocking or base64 encoding, not a Gmail issue. For Gmail-specific signature setup, see the Gmail email signature guide.

Cause 7: Dark mode breaking image visibility

As of 2026, dark mode is on by default for roughly a third of users across iOS and Android, and it’s widely used on Outlook desktop too. If your logo or photo disappears in dark mode, the cause is almost always one of two things:

Problem 1: Dark logo on a transparent background.If your logo is a PNG with a transparent background and the logo itself is dark-colored (black, dark navy, dark grey), it will be invisible on a dark email background. The image is technically loading — you just can’t see it.

Problem 2: Email client inverting colors.Some versions of Outlook in dark mode actively invert image colors that don’t have an explicit background declared. This can turn your dark logo white and your white logo dark — which sounds helpful but often produces ugly results.

How to fix dark mode image problems

• Use a PNG with a white or light rectangle behind the logo. Not truly transparent — give the logo a white background area. This prevents it from disappearing on dark backgrounds and prevents color inversion.
• Add a background color to the image container cell. In the HTML, set the table cell containing your logo to background-color: #ffffff. This gives the logo a visible background regardless of the email background.
• Create a light and dark version. If your brand requires it, create two versions of your logo (one for light mode, one for dark) and use CSS media queries. Note: Outlook ignores most CSS media queries, so this technique works better for Gmail and Apple Mail than Outlook.
• Test it yourself. Enable dark mode on your phone or computer, open your email client, and send yourself a test email. This takes 60 seconds and saves a lot of guesswork.

Cause 8: Firewall or corporate proxy blocking external images

In corporate and government environments, IT departments sometimes configure network proxies and firewalls to block outbound HTTP requests from email clients to unknown external domains. The result: images hosted on your domain don’t load for recipients behind that corporate network, even if the image URL is perfectly valid.

This is most common in:

• Government agencies and defense contractors
• Large financial institutions
• Healthcare organizations (especially in the US, due to HIPAA)
• Schools and educational institutions

How to diagnose: if images work for some recipients and not others, and the ones who can’t see them all work at one organization, a corporate proxy is likely the issue.

There’s not much you can do to fix this on your end, but a few things help:

• Host images on a major CDN (Amazon CloudFront, Cloudflare, Google Cloud Storage) rather than a small personal server. Large CDNs are more likely to be whitelisted by corporate proxies.
• Always include good alt text so the text fallback is meaningful.
• Accept that for a small subset of recipients in high-security environments, images will never load. Design your signature to work fully without them.

For a complete guide to building Outlook-compatible signatures with correctly hosted images, the Outlook signature guide and the Gmail signature guide cover each client’s specific requirements.

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