Thanks, John. Some comments interspersed below.
On 15-Nov-07 13:46:14, Jon Dye wrote:
On 15/11/2007, Ted Harding ted.harding@nessie.mcc.ac.uk wrote:
My question is: What (if any) is the relationship between
<whatever.my.sendmail.uses>
and
<whatever.my.ISP.uses>
??
Does <whatever.my.ISP.uses> take the email address from the "From:" header in the email? From the "envelope-from"? Or does it uses its own version, as in (e.g.):
It should use the envelope-from.
That could be useful! How definitive is that?
One aspect of the background to this question is that, when I try myself to do a (test) manual SMTP dialogue with one of the remote domains mail servers, while I may well get through and successfully send the mail, on many other occasions I will get a response to "mail from:" on the lines of
mail from: Ted.Harding@manchester.ac.uk 451 4.3.2 Please try again later
which will be repeated indefinitely if I keep trying. So I'm wondering if it may be a negative response to the email address used in the "mail from:" request, or has some other reason.
When receiving the temporary rejection you are supposed to retry later. This is normally because of something like too much load on the server or a (temporarily) full disk.
I understand that. However, at times I've retried every 5 minutes or so for up to 10 times, always with the same result. (I use manual telnet to port 25 on the remote server, then doing the EHLO ... / mail from: ... / rcpt to: ... [if I get that far] / ... manually).
It could also be that the mail server may have greylisting of some sort. Basically this is a scheme where the first time you connect to send email the server tells you to try again later. When you retry (with the same from and from the same server) it lets the mail through. The thinking is that spam sending mail bots won't bother with the retry and will just fail. The problem is that some legitimate servers do the same.
Yes,I know about grey-listing (which is probably in place at the far end). It seems to me, though, that the above failure of re-tries possibly rules out grey-listing, since it should respond positively to the next try or two.
[And, by the way, how should I interpret the error message 451 4.3.2 Please try again later ??]
It basically means that the server can't accept email now but that it should be able to at some point so you should try sending it again later (e.g. re-queue it for delivery).
Yes, 451 is supposed to indicate
451 Requested action aborted: error in processing
If I'm not mistaken (though I could be ... ) the "4.3.2" is an instance of the RFC 3463 status nessages class:
X.3.2 System not accepting network messages
The host on which the mailbox is resident is not accepting messages. Examples of such conditions include an immanent shutdown, excessive load, or system maintenance. This is useful for both permanent and persistent transient errors.
which, I guess, could also be valid for a grey-listing refusal.
Hmmm ... Ted.
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