On Mon, 2005-05-16 at 22:00 +0200, Alexander Dalloz wrote:
> > By using a server with a lower MX priority.
>
> But how is that transparent to the clients? That was a criteria for
> Cosme. And I think he means clients trying to send mail.
If the lesser preferred MX is working, the message won't be deferred and
no warning will be sent to the original sender.
> If
> mx1.domain.tld is off which is used by the clients for SMTP, how does it
> automatically switch to mx2.domain.tld without user intervention?
"It" meaning the SMTP client? It just does, at least all SMTP clients I
had the pleasure of managing so far do. E.g. from the postfix smtp(8)
man page:
The SMTP client looks up a list of mail exchanger addresses for
the destination host, sorts the list by preference, and connects
to each listed address until it finds a server that responds.
Only if it doesn't find one it can connect to, or if an error occurs
after it did connect, the message will be deferred and retried, with
notifications starting to go out after 4 hours, etc.
> But as said before in this thread: properly configured MTAs will
> retry to deliver up to 5 days at least.
But not everybody wants to wait several days for their emails. Over
here, people start jumping up and down if there's more than 30 minutes
delay...
In my experience, the SMTP/DNS combo is a pretty good HA design all in
itself. Just use multiple identically configured mail servers, and give
those you don't "normally" want used a lower MX preference. The rest
comes automatically, completely transparent to email senders and
recipients.
Cheers
Steffen.
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