Indeed. So it would seem I have been lost in the dark. Thanks for sharing that reference, makes sense now. Purely a sending mta configuration issue, nothing more complex than that.
-Andrew On 7/10/2021, at 19:04, Viktor Dukhovni <postfix-us...@dukhovni.org> wrote: > > On Thu, Oct 07, 2021 at 06:50:22PM +1300, AndrewHardy wrote: > >> Looks like as long as STARTTLS is present in the server response then >> it doesn’t matter if it’s a hyphen or space and the s_client.c library >> suggests it just looks for that keyword so that confirms it. Helps to >> tell it to encrypt outbound ;) > > In you struggle to explain unexpected symptoms, you've managed to grasp > at non-existent straws. > > https://datatracker.ietf.org/doc/html/rfc5321#section-4.1.1.1 > ... > Normally, the response to EHLO will be a multiline reply. Each line > of the response contains a keyword and, optionally, one or more > parameters. Following the normal syntax for multiline replies, these > keywords follow the code (250) and a hyphen for all but the last > line, and the code and a space for the last line. The syntax for a > positive response, using the ABNF notation and terminal symbols of > RFC 5234 [7], is: > > > https://datatracker.ietf.org/doc/html/rfc5321#section-4.2.1 > ... > The reply text may be longer than a single line; in these cases the > complete text must be marked so the SMTP client knows when it can > stop reading the reply. This requires a special format to indicate a > multiple line reply. > > The format for multiline replies requires that every line, except the > last, begin with the reply code, followed immediately by a hyphen, > "-" (also known as minus), followed by text. The last line will > begin with the reply code, followed immediately by <SP>, optionally > some text, and <CRLF>. As noted above, servers SHOULD send the <SP> > if subsequent text is not sent, but clients MUST be prepared for it > to be omitted. > > For example: > > 250-First line > 250-Second line > 250-234 Text beginning with numbers > 250 The last line > > In a multiline reply, the reply code on each of the lines MUST be the > same. It is reasonable for the client to rely on this, so it can > make processing decisions based on the code in any line, assuming > that all others will be the same. In a few cases, there is important > data for the client in the reply "text". The client will be able to > identify these cases from the current context. > > [ Note that Postfix uses the reply code from the last line of a > multiline reply, and on rare occasions (IIRC only in postscree(8)) > violates the requirement that the code be the same on all lines, > putting the definitive code last. Some clients may not understand > the response code correctly, but such is life in the trenches. This > should only ever be observed in negative replies to botnet clients. ] > > -- > Viktor.
