$ echo -e 'This is a test message\nBlah\nBlah\nBlah' | openssl smime  -sign -signer test.crt -CAfile CA.crt -inkey test.key -outform SMIME 
MIME-Version: 1.0
Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg="sha1"; boundary="----9C04CF8488794540BEE01DC33D6A0FF4"

This is an S/MIME signed message

------9C04CF8488794540BEE01DC33D6A0FF4
This is a test message
Blah
Blah
Blah

------9C04CF8488794540BEE01DC33D6A0FF4
Content-Type: application/pkcs7-signature; name="smime.p7s"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="smime.p7s"
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------9C04CF8488794540BEE01DC33D6A0FF4--