On Tue, 7 Dec 2004, Philip Hazel wrote:
> I cannot remember if the string was all one single-line response, but if
> it was, SMTP mandates a maximum line length.
>
> reply line
> The maximum total length of a reply line including the reply code
> and the <CRLF> is 512 characters. More information may be
> conveyed through multiple-line replies.
On the other hand we know that certain rather popular quasi-SMTP
implementations get upset by multi-line replies. So it's hard to know
what to do for the best.
When we originally formulated our replies, we were quite chatty, like
(to take just one sample at random):
message = We could not verify your purported envelope sender, \
$sender_address.\n
This usually means the sender address does not exist or is blocked.\n\
Or it could be a misconfiguration of the sender's mail server \
or DNS,\n\
in which case you should contact your local network administrators.
and so on. But we now know that this fails to get the message over to
a certain class of (otherwise-bona-fide) users.
We have actually havered a bit - at one time trying to avoid giving
valuable clues to spammers, and inevitably leaving bona fide victims a
bit in the dark - at other times trying to inform bona fide victims
what their problem is, while rather relying on the spammers not
bothering to analyse the results that we send them.
I was considering putting a URL into a modest-length single-line
reply, and preparing response pages on the web server for the more
popular faults. I wonder whether that URL needs to be parameterised,
so that the relevant values can be plugged-in to the resulting page?
Possibly overkill...?
all the best
