I'm looking at what would be required to add LMTP support to Exim, but I've
gotten a bit confused. Hopefully the people who actually want this support
will clear it up for me.
First, I'm basing all of this on RFC2033. I've also looked at binmail and
smtpfeed as example "lmtp servers" (if that's the correct term).
The problem is that while RFC2033 seems to talk of LMTP as a TCP-based
service, binmail and smtpfeed want to talk it over a pipe between the MTA
and the delivery agent. From looking at the newer releases of sendmail,
mail.local now works in the same way. This is not documented in the RFC,
nor can I seem to find references to using LMTP over a pipe.
In this respect, the difference between using a regular external delivery
agent with the pipe transport and using LMTP is that with LMTP you get
per-recipient delivery status.
The most recent request for LMTP support suggested that it would be as easy
as "adding an lmtp flag to the smtp transport". This would be the case if
programs like binmail and smtpfeed were proper daemons and listened on a
well-known port. LMTP is similar enough to ESMTP over a socket that you'd
only be dealing with a couple of protocol verb changes and handling the
results on a per-recipient basis.
Unfortunately, using it over a pipe is a whole different matter. The SMTP
transport doesn't have any code in it for working with pipes, so there would
be a whole bunch of code duplication here. One might say that it was easier
to add LMTP functionality to the pipe transport, but then you have to take
all of the ESMTP protocol code from the smtp transport and transplant it
into the pipe transport. Neither option makes sense to me.
So, if you are interested in LMTP support, please mail me and let me know
how you are using it, whether it's over a socket or a pipe, and where I can
find info describing how LMTP changed from a TCP service in the RFC to a
pipe service in implementations.
Thanks.
--
j.
James FitzGibbon (JF647) james@???
EHLO Solutions Voice/Fax +1 416 410-0100
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