Do any Identity-based Encryption Systems support messaging between domains? Identity Based Encryption is covered under RFC 5091 (specifying the algorithm), 5408 (specifying data structures), and 5409 (using IBE with Cryptographic Message Syntax). However, every IBE implementation that I've seen and used are nothing more than glorified web-mail systems.

Do any existing IBE systems allow secure messages to be sent from one domain/realm to another? Is there any compatibility between vendors?
I've now spoken with representatives from two IBE vendors. The Voltage system allows "federation" by which one Voltage appliance can exchange system parameters with another Voltage appliance. It's not clear if this is done using RFC 5091, RFC 5408 and RFC 5409. The other vendor does not support such a mode of operation.