[1.6] Used to indicate the security options requested for the receipt.
Default Value"signed-receipt-protocol=optional, pgp-signature; signed-receipt-micalg=optional, sha1, md5"
Only supported for Version 1.6.
By default, the adapter will request that the receipt be signed with an OpenPGP signature over an SHA1 or MD5 hash (if these algorithms are supported by the server).
Set ReceiptSecurity to an empty string to request an unsigned receipt.
The string format is that of the Disposition-notification-options HTTP header, as specified in RFC 3335.
This property is not available in the Receiver.