> First, let me say that I haven't read the draft, and don't intend to. > So, if you want to ignore my comments (questions really) feel free. Fascinating. Although your detailed understanding of how this works is fairly far off the mark, you nevertheless have suggested a viable approach that I, at least, hadn't considered. > But from what I have picked up from the (smallish) number of messages > from an even smaller set of people (no great surprise, fax is dead > technology, who cares???) on the ietf list in the past day or so, I > surmise that this protocol work something like the following. At least part of the problem is that the potential use of this stuff extend far past FAX. > It sounds as if what is being proposed is that the SMTP client > sends > RCPT TO:<address> "I want 1200 dpi" It is more like "RCPT TO:<address> "tell me what address can handle:" > Then the SMTP server says > 250 OK More like: "250 address can handle 1200 dpi". > ... > If this is how it works, I don't understand why people are talking about > doing RSET? Surely the protocol isn't built in a way where the server > says "no" to a request, and yet still includes the address in its list > of recipients. it can say "recipient accepted but capabilities are unknown" > Keith's operational plan can be done by sending RCPT TO (where he would > send RCAP) and terminating the sequence with RSET. This way the RCPT > TO acts just as the RCAP would act in his model (as I understand it). > Sure, it isn't as clean by any means, and makes the server do a little > extra work, as it doesn't know the RCPT TO's aren't real ones when it > receives them, but as a trade off, it seems OK. Ah. Using the first round of RCPT TOs as capabilities checks only and sending the RSET unconditionally is really quite cute. It still has the added complexity of having multiple commands per recipient, but now it is the same command repeated, which eliminates a bunch of the edge conditions and makes the silly states very silly indeed. > Others who prefer just to send and see what arrives, just do that, and > it all works the way they expect, with down grading, so the data only > ever needs to be sent once, or with separation of capabilities in the > cases (I am guessing this probably doesn't happen often, and most times > a server will offer the same capabilities to all addresses it can handle?) I suspect there will be cases where the capabilities will be the same and others where they are quite different. Ned