Zimbra as a backup MX

[LMStone]

I'm hoping that the particular point you're getting at will be rendered moot by the spam filters and RBLs in Zimbra, which is a question I forgot to, or didn't think to ask originally... that is will ZCS be filtering as spam on the backup MX? I imagine RBL would come into play since that happens way before content filtering.

If somebody sends non-spam to an invalid address I'm sure they'd like to know, but spam should get silently dropped as it does now.

Sure, spam filtering will cut down the traffic, but no spam filters are 100% effective. Plus, if you are not getting any spam, you probably are getting "false positives" (i.e. legitimate email flagged as spam) which can be worse.

And unless you are syncing the SpamAssassin Bayes databases between the two boxes, the backup MX will likely be less effective at filtering spam than the primary, since the primary will get more spam (autolearn) and the users there will be using the Junk button on the web UI.

Our system gets about 6,000-10,000 emails per day. And this is after we filter out traffic at the firewall via RBLs, anti-virus, anti-spam, and anti-phishing (the firewall drops about 50,000 emails per day via RBL blocks). Even with all that filtering at the firewall, about 10% of the remaining traffic is filtered out by Zimbra as spam/virus emails.

So, for us, any amount of backscatter would be a big deal, hence, my tenacity at trying to make you a convert to recipient verification! :-)

All the best,
Mark

[Robert Mortimer]

We use Sendmail as our backup server
There is a thread on configuring it to check addresses against zimbra.
If you set up local LDAP and sync against Zimbra LDAP you could automatically keep a local copy of the mail user data base. After that you are on to the Sendmail HOW-TOs to get anti-spam etc.

Sendmail is not as memory hungry as Zimbra as it is purely an MTA

Alternatively you could configure a Community Edition and replicate the Postfix config on a standard Linux install (against a local replicated LDAP)