Email signature image is too large - how to fix a slow or broken email signature

If your email signature has a logo or photo in it and your emails are slow to send, showing a broken image icon in some clients, or occasionally landing in spam - the image in your signature is probably the problem. Email signature images need to be tiny to work reliably across all mail clients. Most people set them up once with whatever image is to hand and never think about it again.

Here is what actually works.

What size should an email signature image be?

• Logo or company banner: max 300-600 pixels wide, under 50 KB
• Profile photo: 100 x 100 pixels at most, under 30 KB
• Full-width banner: max 600 pixels wide (the standard email column width), under 80 KB

These numbers feel tiny, but emails are rendered in narrow columns. A logo that appears at 200 pixels wide in a signature has no reason to be a 2000-pixel source file. Email clients scale it down and everything above that resolution is wasted data that slows down every send.

How to resize your signature image

Open Image crop on toolit and crop your logo or photo to just the area you actually need - no extra whitespace, no unnecessary background. Then drop the result into Image compress and compress to JPEG or PNG depending on whether you need transparency.

For a logo with a transparent background, use PNG and compress aggressively - PNG compression is lossless so there is no quality trade-off. For a photo, use JPEG at 75-80% quality. The output will be well under 50 KB for anything signature-sized.

Why large signature images cause problems

Slow sending: Your mail client has to upload the image attachment every time you send an email. A 500 KB logo attached to every email in a day of correspondence adds up fast.

Spam filters: Emails with a high image-to-text ratio, especially large image files, trigger spam scoring algorithms. A lot of spam is image-heavy because spammers put their message inside images to avoid text filters. Your signature image pushes your legitimate email toward that pattern.

Broken images in some clients: Older email clients and corporate mail systems sometimes block or fail to render large inline images. If recipients see a broken image icon where your logo should be, file size is often the cause.

Mobile rendering issues: On mobile, email clients sometimes refuse to render very large inline images or render them in a way that breaks the email layout entirely.

PNG vs JPEG for logos

If your logo has a transparent background - text or icon with no background fill - use PNG. JPEG does not support transparency and will add a white or grey background fill to your logo, which looks wrong against colored email backgrounds.

If your logo is on a solid white background and transparency does not matter, JPEG at 80% quality gives you a smaller file. Use Image convert on toolit to switch between formats if needed.