With 2 gateways, that's 250K per server
Why two gateways? there is only Imail and one MX gateway.
The original suggestion was to use two gateway servers. IMail and two MX gateways.
-- half the load, minus web messaging and such. Plus, a gateway can tolerate higher CPU usage (users won't be connecting via POP3, so they won't notice the CPU usage). Also, with 2 gateways, if IMail chokes on one (receiving more E-mail than it can handle), the other will automatically be used.
but Imail, like any mail machine, chokes dominantly with disk congestion, so 500k msgs received by the gateway, queued, logged, unqueued and SMTP-sent to Imail is about the same load as Imail itself receiving, logging queuing, unqueueing, logging, writing to perhaps large mbx files on fragged disks.
The load is similar, yes (which was part of the reason for suggesting two gateways). However, without the load of web messaging and POP3, which both use disk IO extensively, the load on the gateway server will be somewhat less than the primary mailserver.
So where's the benefit of a gateway? (for the lurkers)
1. a gateway that rejects the usual 70+ % of inbound that is spam, that's 70% less on Imail, the biggest contribution by the gateway. A gateway that doesn't reject anything is hardly worth the effort.
That is a definite advantage of a gateway -- if it blocks 70% of the spam, the load on the primary server goes down significantly. Between the 70% reduction in volume, and the elimination of the scanning on the primary server, it will have a ton of free resources after adding the gateway(s).
2. the SMTP send/receive between Imail and the gateway excludes DNS query delays and SMTP-over-internet session delays, so Imail's send/receive sessions are much shorter, occupying less memory. A benefit, but not nearly as large as 1.
3. Imail outbound queue is always 0 since it drops outbound mail on the gateway in 1 or 2 seconds. Of course, this situation arises only if IMail doesn't have internal problems sending the outbound queue, which happens too often, but less so with a gateway.
4. if Imail can manage to send its outbound queue to the gateway, then any of it that is undeliverable by the gateway and gets deferred to the gateway's queue doesn't occupy Imail queue, Imail retrying, relogging, etc, etc.
Very true.
-Scott
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