On Thu, Feb 09, 2006 at 08:51:56AM +0100, Angel L. Mateo wrote:

SMTP is fine. The advantage of LMTP over SMTP is that it eliminates the requirement for a queue on the mail store (i.e. "Postfix 2" above). This is because it allows selective rejection of mail after the body has been received.

For example, say an incoming message arrives at the mail store with the following envelope:

MAIL FROM:<sen...@somewhere.com> RCPT TO:<use...@example.com> RCPT TO:<use...@example.com> RCPT TO:<use...@example.com> DATA (message body) .

It may be that the mail store is able to deliver the message to user1, has a temporary error when delivering to user2 which needs to be retried later, and has a permanent error when delivering to user3.

With SMTP, the mail store can only give a single response after the message body, so it is forced to accept the mail with a 2XX response code, keep the message in a local spool queue so that it can retry later for user2, and generate an outbound bounce message for the failed delivery for user3.

With LTMP, the mail store can generate separate accept/reject response codes for each recipient. As a result, the sending MTA retains responsibility for retrying and bouncing; the mail store doesn't need any queue runner daemon, not does it send any bounces. This gives you one less mail queue to monitor and manage, and in the case of Cyrus, keeps the code base simple.

Regards,

Brian.