Outlook signature images showing as attachments: fix

When signature images arrive as attachments, it is because classic Outlook embedded them in the message instead of linking to them. Recipients then see files like image001.png, a paperclip icon, or both. The fix is to use a signature whose images are loaded from a public HTTPS address, so nothing is embedded.

This is one of the most repeated Outlook questions on Super User and Microsoft Q&A, often with a twist: "only when I reply", or "only on iPhone".

Why it happens

When you insert a picture into Outlook's signature editor from your computer, Outlook copies the file into the signature folder and sends it as an embedded (inline) attachment with every message. Whether the recipient sees it inline or as a separate file depends on their mail app:

• Many apps show it inline but still list it as an attachment.
• Some phone apps and webmail list each image as a separate file.
• Recipients' attachment filters may flag every message as "has attachment".

Fix 1: use linked (hosted) images

1. Upload each image (logo, headshot, social icons) to a public HTTPS address. It must load in a private browser window without logging in.
2. Build the signature in HTML with <img src="https://..."> tags and set width and height on each image.
3. Paste the signature into Outlook as formatted content.

Outlook sends the link instead of the file. The recipient's mail app fetches the image when they open the message.

The trade-off is that some recipients block remote images until they trust you. Give each image short alt text, and keep your name and phone as real text.

Fix 2: check how you are replying

If attachments appear only on replies, the reply may be in plain text or rich text format. Plain text drops images entirely. Rich text (RTF) can turn them into attachments. Set replies to HTML under File > Options > Mail > Compose messages. See Outlook signature in plain-text replies.

Fix 3: rebuild after a template change

Old embedded copies stay in the signature folder. After switching to linked images, delete the old signature in Outlook and paste the new one so no embedded copies remain.

Where Sendoff fits

Sendoff hosts every signature image on a public HTTPS address and outputs linked images with width, height and alt text set. Copy the signature from the Outlook signature generator and paste it. Nothing is embedded, so nothing arrives as an attachment. If you already have an HTML signature, paste it into the free signature checker to find embedded or local images.

FAQ

Will linked images show for everyone? Not always. Some recipients block remote images by default. Embedded images avoid that but cause the attachment problem. Most businesses prefer linked images with good alt text.

Can I use base64 images instead? Gmail and several other clients do not display base64 data images in signatures. Use hosted files.

Sources

• Super User, "Email Signature is creating attachments": https://superuser.com/questions/1135924/email-signature-is-creating-attachments
• Microsoft Q&A, "Why do icons within a signature appear as attachments": https://learn.microsoft.com/en-us/answers/questions/4674946/why-do-icons-within-a-signature-appear-as-attachme