Thanks all for your answers :)
Let me give you additional details :
When I do send an encrypted & signed email to this user using "Sign" and "Encrypt" buttons in Outlook , he does receive it as an encrypted & signed email, as shown below in Outlook 2010
PGP Pop-Up indicated me that it's been decrypted, and the signature has been verified
When this user is sending me an encrypted & signed email using "Sign" and "Encrypt" buttons in Outlook, I do receive it only encrypted, and not signed, as shown below
PGP Pop-Up indicates me that yes it's been decrypted, but no clue about the signature being verified
But when this same user is sending me a signed only message using the "Sign" button in Outlook, I do receive it signed.
What I'm trying to figure out is why encrypted & signed message are delievered only encrypted, and not signed.
Cheers,
Julian