01What it looks like
Recipients may see a paperclip, a separate image file, or a blank box where the logo should be. The message still sends, but the signature looks unprofessional and some clients block the attachment.
02Outlook and attachments
Classic Outlook can treat VML-wrapped or locally embedded images as attachments. Microsoft documents using the Image button in the signature editor with a linked picture when possible.
Dragging a file into the signature box often embeds it. Use Insert picture from a web address instead.
03Apple Mail on Mac
Pasting images from the clipboard can embed them as attachments on send. Prefer a signature whose images are already on https links, then paste rendered HTML into Mail › Settings › Signatures.
04Switch to hosted images
Export or upload the logo as PNG or JPG
Host it on a public https URL (Hilsio does this when you build a signature)
Rebuild the signature HTML with <img src="https://…"> and width/height attributes
Paste the rendered signature into your client's settings and save
FAQ
Why does my email signature send images as attachments?+−
The image was embedded in the message instead of linked. Dragging files into the signature editor, base64 data, or certain VML markup in classic Outlook cause this. Use linked https images with explicit dimensions.
How do I stop Outlook from attaching my logo?+−
Remove embedded images from the signature, host the logo on https, and insert it by URL or paste a table-based signature built with linked images. Avoid dragging pictures from your desktop into the signature box.
Do hosted images count toward Gmail's size limit?+−
Yes. The img tag and URL still count toward Gmail's 10,000-character limit, but they are far smaller than base64 blobs. See the Gmail too-long fix guide and use the size meter.
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