one more thing - if a client sends BDAT when the server hasn't sent
2xx to MAIL and at least one RCPT, it's perfectly reasonable for the
server to abort the TCP connection, since even if the client has
additional messages to send it's not likely to resync anyway.
I suppose a server that wanted to be kind could accept NNk bytes of BDAT
(discarding the data and returning 5xx to each) before closing the
I think the requirement to check MAIL/RCPT responses is on the client
but an implementation note for the server about the potential synchronizaiton
problem also seems appropriate.