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Creating open SMTP relay

Posted on 2014-07-25
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Last Modified: 2014-07-25
Good Morning,

I have come across a bit of an issue that I'm hoping you experts can help me with. I have a batch of customers which have recently changed their internet connections to an ISP that has no SMTP relay on it's network. This is quite a big deal so I've decided to turn an old Exchange 2007 box into an open SMTP relay in my customers can use to relay mail out onto the internet. The plan is to have the SMTP relay at my offices for better control and this is on a different network/ISP altogether.

I have created an A Record smtp.domain.co.uk and pointed at our Public IP address so I'm guessing that's set up correctly.

Does anybody have any ideas on how I can achieve this? I do have a Public IP range for the customers networks so it doesn't have to be totally open as long as these public IP's can use our server as an smtp relay I can't see it being a problem.

Many Thanks,

Chris.
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Question by:ChrisRoberts86
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Miguel Angel Perez Muñoz earned 500 total points
ID: 40218700
Creating an open relay causes spamers uses to send spam. And, your server will be listed on blacklisted or as a open relay.
Consider ask to ISP for a smtp relay provided by. Per example, Telmex does not permit dynamic ip address send smtp but provide a relay with user and password.
Finally if you want to create your relay, this post may help you: https://confluence.atlassian.com/display/JIRA/How+to+Set+Up+SMTP+Relay+in+Exchange+2007
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Expert Comment

by:David Atkin
ID: 40218759
I'd strongly advise against using your Exchange for an open relay as well.

Have a look at other third party SMTP relay companies.  I use http://www.authsmtp.com/ for a couple of my linux servers.  There is an annual price for the service but I've found them to be reasonable for what I do.  Double check before signing up though!

Another suggestion is tempting your customers with an email filtering service. You'll get best of both worlds here, your customer will get reduced spam from inbound filtering and they'll get an outbound smtp relay.  I have had a good experience with Spambrella (UK Based).

If you are going to go ahead with creating a relay then make sure that you define your customers external IP's so that you don't get random spammers using it.
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Author Closing Comment

by:ChrisRoberts86
ID: 40218820
Many thanks for this, I was able to create a locked down relay for the public IP address range I needed as well as adding some encryption to it.
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Expert Comment

by:Mohammed Khawaja
ID: 40218823
What you should do is convince/educate your clients to use SMTP servers but ensure to authenticate.  If you wish to let your users use your Exchange server then ensure to configure your server to require authentication as well as ensure to only allow relay for specific IPs (i.e. your clients Internet connection IP).  Even then your customers may experience issues using your Exchange server if there are SPF, reverse DNS records, etc. are missing.  Best is to use a provider that sells services such as SMTP.
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