Re: [Exim] Re: Caching DNS and Exim (Vadim Vygonets)

> All of our emails are unique... So we do not have multiple recipients on
> any message. So, this is a solid 6,000,000 messages at about 10GB
> outgoing. Outgoing is the only time DNS caching matters, we shouldn't
> consider incoming messages.

I verify sender adresses, which also causes quite some DNS requests.
Not being able to deliver due to DNS troubles is bad, not accepting
is worse.

> How much ingoing and outgoing.. The 16GB could be deceiving.. You should
> look at quantity of messages not counting the size at all.

Of course, but most large systems have a typical mix of sizes and I
found that more people count traffic than messages, that's why I usually
give traffic. We have up to 400.000 arriving messages with about 60%
for local users and 40% outgoing. All incoming traffic is routed by
two MX machines to either mailbox or outgoing queue machines. Two more
MX machines are already ordered, because LDAP appears to eat quite some
CPU time (the system is entirely LDAP controlled).

Concerning delays: Any failing service that increases the time of SMTP
transactions increases the number of connections and as such the number
of processes. That's what can kill a busy system.

Michael