Sendmail does, qmail uses a – instead of a +, don’t know about postfix. That probably covers 75% of the mail transport installations out there. I’d still rather key off of a subject line, since any mail filtering software can make decisions based on the subject.

Any idea whether most/all mail transports properly handle this?

Using a header should work as you’re using a program to read the mail. Where it might not work is if a human being was reading the mail and their client didn’t understand to use the header. Most wouldn’t and probably wouldn’t have any kind of choice to allow “preserving” the headers on a reply.

But, YES, the XML-RPC and SOAP protocols should be useable on more than just HTTP. Mail is but one other choice.

-Bill

Now, does the From: address really need to be a special one? That would be bad for people who don’t have that type of control over their mail systems (like anyone who doesn’t own their own mail server). How can we get around that problem?

And just thinking about it a little bit, but can anyone think of any value in having xml-rpc via NNTP?

Reply-to: reply+A035882BC9@address.caller.machine

I would actually be inclined to do this with the subject line. For example, specify that the reply subject is the exactly “Re: ” + the request subject.

Alternately, the sending email address can be munged to have the message ID as a portion. If there were any bounces from misdirected email, then there would be some way to correlate that bounce with the correct call.

eric

Reply-to: reply+A035882BC9@address.caller.machine

The Mail Transport Agent should only use the part before the ‘+’ sign to route the mail, and leave the Mail Delivery Agent to switch on whatever comes after the ‘+’ (I use this in conjunction with procmail). You then specify that the XML-RPC reply go to the Reply-to: address.

Another way would be to use RFC-822 extention headers, for example:

X-XML-RPC-Request-ID: A035882BC9