'Problems validating this signature' on signed emails in OWA
windows
Symptoms
Signed messages open but show a signature validation error.
Likely cause
*.mail.mil is not in IE Trusted Sites.
Fix
1. IE > Tools > Internet Options > Security > Trusted sites > Sites.
2. Add https://*.mail.mil > Close > OK.
For other branches, follow win10smime.pdf.
Sourced from militarycac.com. Rewritten for clarity.
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