Q: What was that awful problem with the WISCVM gateway talking to the CSNET Relay?
A: Mr. Protocol is genuinely fond of this question. It is a sterling illustration of the necessity of adhering to protocol in all things.
In the SMTP mail exchange protocol (which was shamelessly based on the old NCP FTP protocol), there is a provision to allow the reply codes (which are rarely seen by the user) to extend over several lines. For a single-line reply, the format is: “three-digit number, followed by a space, followed by text of reply”, (for example, “504 text of reply”). For a multi-line reply, the single space is replaced by a hyphen on all lines but the last one. Mr. Protocol calls particular attention to the fact that the format of a continuation reply line is: “three-digit number, hyphen, text of reply”, (for example, “504-text of reply”) and NOT “three-digit number, space, hyphen, text of reply”, (for example, “504 -text of reply”).
Mr. Protocol has a long memory (a necessity in his calling) and remembers that in the days of “iron men and wooden wires”, there were at least one, and possibly several, important sites which believed that either form of continuation was acceptable, no matter what the protocol said. Mr. Protocol was horrified but there was little he could do. Consequently, he allowed a mailer (it was an FTP mailer in those days) to be installed which would accept either form. This was perfectly correct: Mr. Protocol’s genteel watchword is: “Accept anything from anyone, but send only what is correct”
[N.B.: Mr. Protocol is aware of the pragmatic attitude evinced by the phrase “important site.” If one receives many messages which break one’s mail service, one is more likely to fix one’s server than if such messages are rarely received. Consequently “important site” is often defined to mean “A site which it behooves us to talk to correctly, lest our mail service break.” Mr. Protocol believes, of course, that one should speak correctly to everyone, but he also believes that a sense of priorities is not out of place.]
Many years later, the WISCVM gateway was created, with a whole new set of software. And, strictly according to protocol, they sent out a reply line (in the event of mail failure) which was of the form: three-digit number, space, hyphen, text of reply. This was NOT a continuation line and was perfectly legal. The SMTP mailer on CSNET -RELAY, however, was still being overly forgiving and believed that it WAS a continuation line, and sat around idly waiting for the rest of the reply. Situation: deadlock. Mr. Protocol cried into his tea and caused the mailer to be fixed. It is now less forgiving, but also adheres strictly to protocol. Mr. Protocol feels sad but virtuous, and the mail flows once more.