On Tue, 14 Aug 2001, Manish Jethani wrote:
What is smart host? I am running a local smtp and I am able to send
Things you know (I hope):
When one sends mail, it goes to a mail queue on the mail server (which may be local). The mail server periodically tries to send all mails in the queue. There are cases (destination not reachable, name server error, etc.) when a mail cannot be delivered, and remains in the queue.
Problem:
If the mail server is permanently connected to the net, then there is no problem, because it can try the servers indefinitely until it makes a connection. If it's not however, then we have a problem. If mails cannot be sent when a net connection has been estabilished, then they may have to wait for a very long time in the queue.
Smart Hosts:
Enter smart hosts. They may or may not be smart actually, what's important is that they are connected to the net permanently. Your local mail server can forward all mail to the smart host when it is connected, and then the smart host takes over the job of sending the mail when it can.
Smart?
So what's so smart about these hosts? Basically, by doing NS lookups on the MX record of a destination domain, a mail server can figure out exactly who the mail exchanger for that domain is, and forward all mail for that domain to that host. Thus, if you send mail to 5 yahoo.com addresses and three hotmail.com users, the smart host will split this into two mails, send one to any one of:
mx1.mail.yahoo.com, mx2.mail.yahoo.com, mx3.mail.yahoo.com, mx4.mail.yahoo.com, mta-v18.mail.yahoo.com
in that order, depending on which is available first, and the second to any one of:
mc1.law13.hotmail.com, mc2.law13.hotmail.com, mc3.law13.hotmail.com, mc4.law13.hotmail.com, mc5.law13.hotmail.com, mc6.law13.hotmail.com, mc1.law5.hotmail.com, mc2.law5.hotmail.com, mc4.law5.hotmail.com, mc5.law5.hotmail.com, mc6.law5.hotmail.com, mc7.law5.hotmail.com
in any order.
Can it get smarter?
Kind of! You can manually specify which gateways to use to reach different domains. But never mind about this.
Does that clear things up? If it does, then someone should edit this and convert it to another tute.
Philip