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.
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.
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.
If you google for greylisting you can find the gory details.
[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).
JD