[CentOS] Postfix Questions
feizhou at graffiti.net
Wed Sep 19 01:10:39 UTC 2007
John Hinton wrote:
> I've been running sendmail since the beginning of my online time.
> 1. Did I see that postfix can run sendmail milters?
Yes but different version with varying levels of milter support.
> 2. If so, did I read that postfix can run these separately for inbound
> vs. outbound?
Yes you can apply separate rules for incoming and outgoing emails if
they come from separate ips or ports.
> 3. Can it run like a rbl blacklist on inbound and not outbound?
> 4. If the above is true, does this require separate configurations of
> postfix or is it already set to allow this out of the box?
You will need to configure postfix appropriately.
> My reasoning... I've added a few milters which has drastically cut spam
> due to the extra time spent at the smtp level. For instance, running
> spamassassin takes a couple or few seconds. This bit of delay does in
> fact seem to stop many of the slamming spambots sort of like the design
> of milter-greylist. Except, I don't have to send a temp fail. So, this
> is a good thing. The negative is it also takes longer for my users to
> send mail as it is processed the same way during outgoing.
I do not know what level of milter support is required by your milters
so you may want to check them out. The latest versions of postfix will
have more complete support.
> Also, we run the SpamHaus blacklist. This works pretty good for inbound,
> but from time to time one of our hosting clients winds up on the
> blocklist because they are on a dynamic IP and someone else has recently
> used it for spamming. One could argue that my client should then go
> remove their IP from the blacklist to better insure their email actually
> makes it through any other level of spam filtering on other ISPs. But,
> that's a rosey concept! So, I would prefer to do it at the smtp level
> inbound so I can actually reject that mail while not having the
> embarrassing blocking going on with our users. Yes, this might sound
> like a double standard, but we do not provide connection service so only
> very rarely (never so far) does any virus actually send spam through our
> systems from client applications and I do actually monitor email all the
> time and stop any spamming immediately.
Sure, just make sure they use port 587 and are only allowed to have
their email relayed after authentication and disable filtering rules for
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