SMTP Service Extension for Reliable Delivery
Isode Ltd.
Brooktrout Technology
There is an issue with SMTP that RFC 1047 raised in 1988. The time between a SMTP client submitting a mail object and the SMTP server responding to the request can be arbitrarily long. SMTP addresses this issue by a hack, hoping that the SMTP server responds fast enough and the SMTP client waits long enough to find out if the submission was successful.