email store and forward server

HalCHub
HalCHub used Ask the Experts™
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I would like to put together an  email store and forward server for a number of my clients as a fail over for their email servers.

They are all Microsoft Exchange users and I can build the server using Lunix or Microsoft products.

What open source products do you recomment ?
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Commented:
That rally depend on your funds. If you need corporate solution I would go with MS Exchange 2010 - but it need quite few serwers to work as it should. If you dont want to spend money go with postfix which works good if configured properly. Other open source product was Zimbra but since VMware bought it i dont know if it is still full free product.

Author

Commented:
they are running exchange 2010... I want put up a server which would be a storage of email fail over until they came backup.  I can put an exchange 2010 server too.

I need this for multiple domains.

Commented:
The SMTP service that comes with windows and IIS will do this just fine.  Configure it to accept and relay mail for the customer's domains, and configure the domain to forward to the 'real' mail server.  

A technically complete solution would have your server set up as a secondary MX for the customer's domains.  However, this will make you a target for spammers,vso make sure you have a good anti-spam system in place.  Personally, I recommend ORF from vamsoft (http://www.vamsoft.com)
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Commented:
I would like the "front end server" to be an ubuntu server which will not have knowledge of the domains.

Commented:
I'm much less familiar with Linux, but what you want is still possible.  No matter what you use, the store-n-forward server still needs to know that it can accept mail on behalf of the domains, then it needs to know what hosts to forward the mail to.  So, it has to have *some* knowledge of the domains.

Author

Commented:
does it need to know about individual email addresses too ?

Commented:
No, it will simply accept the message for delivery, then make attempts to deliver it to the appropriate mail server.  Three things to point out here: (1) your server has to be told which domains it can accept mail for; beware becoming an open relay.  But, you probably already knew that.  (2)  being a secondary MX server for a domain makes you a more preferred target for spammers.  and (3), if possible, it would be better if your server had a list of legitimate addresses for the domains.  Otherwise, it will accept *any* address ending in '@mydomain.com", and many mails will suddenly bounce.   This is called 'backscatter', and may get the server blacklisted. As you may guess, items 2 and 3 are related
I agree with most of what BudDurland is saying... *Any* SMTP MTA will be able to facilitate this, so the Postfix of an Ubuntu server will most definitiely work, but it does need to know which relay_domains to "trust"/work for. Being a secondary or tertiary (or whatnow) MX puts a fair amount of resposibility on your organization, as per the RFC specs, not least of which is the spam handling thing... Perhaps not yours to handle, but definitely yours to "enlighten" your customers about (if you don't do some normal anti-UCE/malware checks, they cannot trust your host implicitly... If they do, you'd be a "highway for spam/malware" into their domain... Which would likely just make them ... less than enthused... with the service rendered).

The only thing I might disagree about is that you really don't need to know the individual addresses, just the "next hop" for each domain (and perhaps rely on MX records for that as well), as long as you set your machine up to do _recipient_ verification (a kind of "call-forward" thing to ascertain that the recipient is a valid one). This is inbuilt in Postfix since a while, so should be easily configured. The extra network traffic incurred is well compensated by the amount of gunk you will simply reject/never handle. Again, this is something you need make clear to your customers, so that if they run really old/deprecated MS Exchange setups (that incorrectly accepts-n-bounces instead of plain reject unknown recipients), they can amend things to a more sane behaviour.

Cheers
--
-- Glenn

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