[TriLUG] OT: DSL for SOHO in Chapel Hill
chrish at trilug.org
Tue Jan 27 16:26:44 EST 2004
On Tue, 27 Jan 2004, Jim Ray wrote:
> Pardon my ignorance. When you set up mx1.* and mx2.*, will each of the two
> redundant mail servers chuck the data into a common black box possibly on a
> third local area network server such that end users keep on using IMAP or
> POP3 without changing any end user settings upon front end server failure?
DNS 101, section 8, "MX Records".
Basically you set up an MX record for each incoming mail server in your
domain. For most small businesses it is enough to have a primary MX
pointing at your real mail server, and a secondary MX pointing at a friend
(or TriLUG's server). Note your secondary must be pre-configured to act
as your secondary (which is usually pretty simple).
Your secondary MX is nothing more than a mail server on some other
network, preferably a different ISP than you, that agrees to relay mail on
MX records have a preference or cost listed next to them. Sender will try
to connect to the lowest cost MX first, then the next lowest, and so on.
Primary MX is preferably the final destination. Secondary MX will accept
mail on behalf of the primary, and then try to relay message to the
primary until it comes back online.
Usually two MX hosts are enough unless you are AOL or some other
relatively enormous mail provider. Even then they usually play tricks by
having a load balancer between a single IP and a farm of mail servers.
Two MX records may then end up pointing at dozens of servers. But that's
another lesson for another time.
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