[CentOS] Recommend Mail Server
christopher.chan at bradbury.edu.hk
Tue Nov 24 03:00:04 UTC 2009
Ian Forde wrote:
> On Nov 23, 2009, at 5:34 PM, Christopher Chan
> <christopher.chan at bradbury.edu.hk
> <mailto:christopher.chan at bradbury.edu.hk>> wrote:
>> Les Mikesell wrote:
>>> You probably really want ldap for that sort of thing.
>> You probably really want to reconsider using ldap for anything that gets
>> loads of changes daily.
> In the case of a mail relay, at one point years back I decided to
> drop (not bounce) all email to bogus recipients at the relay level
> rather than let it get to (yuck) Exchange, which would bounce it. The
> trick was having an updated recipient list. My first thought was to
> query Active Directory for each user, thus getting an up-to-date result.
> This turned out to be a *bad* idea for a couple of reasons. 1) if I
> can't reach AD, mail won't queue up on the relays, which is one of
> their major functions. 2) I'm making the relays directly dependent on
> AD latency. 3) any flood of email from outside can cause a large
> amount of queries against AD, causing a DOS that the relays are
> supposed to shield the internal network from.
> So instead, I found a script to gather the list of users from AD, did
> some modifications and wrote some wrappers. The result? A script that
> runs from cron to get the list of valid addresses, convert them into
> an access file that sendmail (or postfix, in the first case years ago)
> can use instead. There's a little more latency, but as long as I do
> some sanity checking (too many changes? Send an alert and don't change
> the access file) it works just fine. Ldap-based, yes. But loosely
> coupled. A good compromise in my experience...
Precisely why a buffer like this for sites with a very large user base
might want to use cdb. postfix supports cdb and sendmail can get cdb
support from sf.net/sendmail-cdb. Both need the tinycdb library though.
Even mysql/postgresql could do with a break for legit users.
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