How to Fix Email Signature on Outlook

Question

I’m having an issue with Outlook Desktop when trying to add an email signature from an HTML file.

When I open the HTML file and copy the signature, I’m unable to paste it into the Email Signatures section in Outlook Desktop. Nothing happens when I try to paste it. However, the same HTML signature works correctly in Legacy Outlook, where I’m able to copy and paste it without any issue.

I’m also certain this copy-and-paste HTML file method was working a few days ago, but now it no longer works.

Could you please help me understand why HTML signatures can no longer be pasted into Outlook Desktop, and whether there is a supported way to add them?

Answer 1

Hi @Aleksei Alonzo,

Thank you for posting your question in the Microsoft Q&A forum.

According to your concern, the issue is highly due to the difference between how New and Legacy Outlook handle signatures. In New Outlook, signatures are stored and managed in the clouds, not as local .htm/.rtf/.txt signature files like legacy Outlook does.

Therefore, since everything is saved online, the traditional file-based method for importing signatures (like pasting .htm files) cannot be applied to New Outlook. If you want to move your signatures from Legacy Outlook to the New Outlook, there are two methods:

• Recreate your signature in the New Outlook signature: In Outlook, press Command + , (open Outlook Settings) > Signatures > Add
• Copy the rendered signature from Legacy Outlook, not the html source: open the html file in Edge > copy the rendered signature (not view source) and paste it into Outlook signature (open with same steps as above)

For more details and explanation, you can refer to Outlook signature location & how to export, import, backup them

(This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.)

Hope the information may help. If you have any questions or need further assistance, please feel free to share them in the comments on this post so I can continue to support you.    

Thank you for your understanding and cooperation. I'm looking forward to your reply.

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Answer 2

Outlook Desktop has multiple clients with different feature sets and behaviors for signatures. Classic Outlook for Windows still supports rich HTML editing in the signature editor, including pasting complex HTML content. New Outlook clients (including New Outlook for Windows and New Outlook for Mac) have more limited, controlled signature handling and can behave differently from classic Outlook.

From the available information, the supported and reliable approach for Outlook on the desktop is to create or edit the signature directly within Outlook’s built‑in signature editor rather than relying on pasting full HTML from an external file. For classic Outlook, this is done via:

1. File > Options > Mail > Signatures.
2. Select the signature and edit it in the Edit signature box, or create a new one and build/format it there.

This method is the documented and supported way to add or change signatures in Outlook for Microsoft 365 on Windows and avoids issues related to HTML pasting behavior changes between Outlook versions.

If the environment is using classic Outlook and signatures are causing errors or unexpected behavior (for example, the “This is not a valid style name” error when rendering signatures in Rich Text format), switching the message format to HTML and/or simplifying the signature HTML is recommended. In classic Outlook this can be done under File > Options > Mail by setting “Compose messages in this format” to HTML.

If using New Outlook, and pasting HTML no longer works as it did previously, this reflects the client’s current behavior and limitations rather than a supported feature regression. In that case, the supported path is:

• Create the signature directly in Outlook’s signature UI using the available formatting tools.
• Avoid relying on complex external HTML or script‑heavy templates.

For organizations that require centrally managed or advanced signatures, Microsoft recommends using supported roaming signatures or approved signature add‑ins rather than manual HTML pasting.

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References:

• Change an email signature
• Users might get the error "This is not a valid style name" in classic Outlook
• Signatures are not syncing between Outlook Desktop and Outlook Web App
• Delay in sending email in New Outlook for Windows
• Troubleshoot attachment problems in Outlook for Windows