message streaming ?

Hi,
I'm writing my S/MIME application as a SMTP&POP3 proxy. At the moment I read
in the entire email being sent into memory and then encrypt it. Oviously
enough, this is fairly slow and inefficient. I was hoping to possibly setup
a pipeline of sorts where I could just take in chunks of data, encrypt them
and send them off.

I think it should be quite doable as regards S/MIME as the header
information like recipientinfo/originatorinfo etc should be quite small and
could be processed and sent on straight away. After that, it's just a matter
of sending on the encrypted data, chunk by chunk. One possible problem I'd
see would be the initialisation of the content encryption algorithm's IV
each time around.

I haven't looked into doing this in very much detail and was hoping that yee
could possibly tell me is this is doable or not within the current design of
the SFL. I don't want to spend a few days going through code to find out
that it's just not possible.

Thanks,
Gavin