Hello Admins,

I have several years experience with Groupwise and the excellent Mercury/32 Mail Server. Recently I got Zimbra OSE running for my two mailbox office and I like it very much. I now want to move a clients domain away from an ISP to Zimbra.

Currently there are 100 mail boxes at the ISP being accessed from 7 different locations via pop3. All mailboxes are in the same domain *@mydoamain.com.

The ISP does not do any spam filtering or implement DNSBL so the incoming spam is outragous and it's up to each user to deal with it at the desktop with varying degrees of success.

Dispite this awful situation I am getting 'political' resistance to a Zimbra solution. Due to this I must move in baby steps.

Here is what I plan to do and I have a question about it.

My Plan:
Get a static ip address for our office and install a Zimbra OSE server.

Set this new ip address as the primary mx, leaving the current ISP as the secondary.

We have 20 'local' mailboxes at this location so those will come in just normal like. Another location has a 20 mailbox Exchange server and I will 'somehow' (Split Domain) redirect those mailboxes to the remote exchange server. The remaining 60 mailboxes will be redirected to the ISP so that those 60 users will get there mail from the ISP as they always have, those 60 users will see no change in the way things work except that they will get less spam because Zimbra should drop all emails that fail DNSBL.

Please confirm that this is how the mail will flow:

Does the TO: address exist (if not 500 error)
Does the sender ip address fail DNSBL (drop)
Is the TO: address local --> Anti spam/virus --> Deliver to Mailbox {end}
Is the TO: address at the Exchange Server --> Redirect to Exchange Ip address {end}
Is the TO: address at the ISP --> Redirect to the ISP smtp server {end}

My question is: Does Zimbra bring email in check it for spam and virus and then turn around and send it back out to the ISP and Exchnge servers or does it somehow redirect those emails on the fly without bringing them in at all?

Thanks for reading, all comments welcome.