Peering means that both servers share the same MX priority level for
incoming mail only, but only one of the two (or ten ) servers has any
specific mail account. Any peer server will accept the mail, and then
forward to the correct peer using the SMTY VRFY command (has to be
enabled). This does give a backup mail server / redundancy aspet, also,
Peering has no advantage on heavy-lifting of outgoing mail, POP3, or Web
Messaging, all of which have to be handled by the specific Imail server
that holds a specific Imail account.
The real nasty work of SMTP job is not receiving mail, but in sending it.
Imail has to spawn an SMTP process, which then looks up the destination ip
in DNS, wait for that to come back, tries to contact the mail destination,
if unreachable, it retries with secondary mail destination, if fails,
queues the mail for later attempt, etc, etc. if reachable, it shakes
hands, blah, blah, delivers the mail, all at typically erratic internet speeds.
To offload all of that outgoing grunt work to another machine, use the
Imail "deliver through a gateway", where the gateway is at best on the same
local subnet, and you give the gateway's ip address so Imail doesn't have
to do DNS lookups to find the gateway's ip address. Imail drops the mail on
the outgoing gateway ip address quickly and reliably, gets back to work the
more user-reactive tasks such as POP/IMAP and Web messaging sessions.
Len
=====================
>Can anyone out there explain the relationship between 2 peered IMail
>servers? how much load balancing can they accomplish or does the second
>server just handle the occasional overflows and downtimes via a secondary
>MX?
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