The DSN standards (RFC 1891, 1892, 1894) have now been
ready for more than two years. Yet very few mailers support
them. What can be done to get more support?
First a response to Jacob's comment: Last time I went to an
interoperability test, most major vendors of SMTP were supporting DSN.
I'm afraid there are two major obstacles to the widespread use of DSN:
1. the amount of User Agents supporting DSN is low
Yes, but this only explains the inability to request delivery
confirmation. DSNs are very useful even if many clients don't support
them.
Note that there are two levels of support for DSN in MTAs:
1. if they generate nondelivery reports in DSN format
2. if they advertise the DSN SMTP extension, implying that they
support NOTIFY, ENVID, etc.
The first is easier to do than the second.
2. from my experience I know that in a significant number of cases
the problem why DSN is not supported by a company e-mail infrastructure
the firewall that's being used in the real world. In many cases the
firewall has an active mail component, thus limiting the support for
SMTP and extensions to what the firewall provides. And more often then
not the firewall does not support DSN or does not even ESMTP at
all!
Yes, firewalls are a major problem.
We need a clear community statement to the effect that firewalls that
block arbitrary SMTP extensions are nonstandard and broken.
Keith