Hi,
Does this issue happen to all emails when replying? Are you replying to Plain Text messages? If this is the case, please try changing the email format from plain text to HTML and then reinsert your signature to see the result.
If you are already replying to a HTML format message, we may try empty your Outlook Temp Folder to see if it helps. To do this, please follow the steps below:
1. Open your Registry Editor.
2. Navigate to
HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Security
3. Open the
OutlookSecureTempFolder registry key.
4. Copy the path from the key and paste it in the Address Bar in Explorer and press Enter.
5. Clear everything in the folder and then test the issue again.
Please let me know the result.
Regards,
Steve Fan
TechNet Community Support