A user on my system is subscribed to a large volume mailing list. When mail
is sent to the user on my system, it never gets delivered because qmail
bounces it due to an error 553, the server is not in my list of rcpthosts.
I previously passed this off as being a problem on the other end, but it has
been explained to me that large volumes of e-mails are distributed as
follows:
1. Mail list server has 500 identical e-mails to send.
2. It gives that list of addresses to the mailserver, along with the e-mail
message.
3. The mailserver then contacts teh first server on teh list, says "here's
an e-mail message", along with a list of addresses (usually 20 or so).
Sometimes all those addresses are on that server, somtimes not.
4. To stop spam, the receiver then checks the list for at least one valid
receiver. if one is local, it delivers it and any other local mails, then
relays the rest off to the first system in the list left over.
This system, in the overall scheme of things, is designed to reduce traffic
across the internet, because if your network happens to hose 3 of the
domains onteh list, it's able to take a lot of traffic off the internet and
send it internally instead. Also, with mail going out of the country, one
Australian server would end up relaying to other .au hosts, saving taffic
over global pipelines.
Qmail is denying legitimate messages to my users because it doesn't allow
this type of relaying. Why?
-Eric
