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by nsteere

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I wan't to do whatever I can to keep my soon to be mail server from getting black listed and here is the details:

Soon to be created ASP site will be using Exchange 2000.

1. Our application creates an email via SQL Mail
2. Outlook XP or 2000 will send an email to our internal Exchange server for routing out to the various client recipients.
3. SQL Mail will be using a single (gateway) email account to act as the sending user account.
4. All email will be received as coming from that single user accout.

We have implemented this solution at quite a few companies and it works great except one of them has been tagged as an open relay for sending spam and blacklisted. I am afraid that it may have been caused by all that mail sending from one account and made it look like some guy was spamming. The content of our email is not spam. The clients are the CFOs and staff of hospital networks and the email is mereley a notification that a budget proposal has been entered into the main application by other users who want them to be aware of it. I am afraid that the email functions of our ASP site could be a target of spam blocking.

I am also very afreaid of a hacker turning our ASP mail server into an open relay for his spam (I don't know the best way to stop that from happening).

So, after all this info; Does it sound like I have a valid fear and if so, what would be a way to avoid a blacklist?

And: Any link or pointers on preventing my server from being used as an open relay? I know that would get us in trouble.

11 replies

by maxwell edison

Companies get into the "black-list" trouble when they either willingly or, more likely, unwillingly, allow their Exchange servers to be used as a conduit for spam. Open Relay is "enabled" by default, so administrators must initially take the steps necessary to disable the open relay.

See this article titled, "Third-Party Mail Relay (Open Relay) and Microsoft Exchange Server". Not only will it provide you with the step by step instructions on configuring Internet Mail Connector to stop open relay, but will also give you some interesting insight into the open relay/spam issue.

http://rr.sans.org/email/open_relay.php

And there are different steps required to disable open relay, depending on the version of service pack applied. See these links as well. They will provide some nicly illustrated instruction for both.

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Turning Relaying Off In Exchange 5.5 With Service Pack 2 Or Higher:

http://rr.sans.org/email/open_relay.php

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Without Service Pack 1 or 2:

http://support.microsoft.com/directory/article.asp?ID=KB ;EN-US;Q193922&

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Microsoft article, "HOW TO: Prevent Exchange 2000 from Being Used as a Mail Relay in Windows 2000 (Q310380)"

http://support.microsoft.com/default.aspx?scid=kb;EN-US; q310380

(REMOVE SPACES from the pasted URLs.)

by maxwell edison

Actually, after re-reading your question, I stand corrected. While Exchange 5.5 does indeed enable open relay by default, Exchange 2000 does not.

Nonetheless, the provided links to the articles will certainly explain the process - especially Microsoft article Actually, after re-reading your question, I stand corrected. While Exchange 5.5 does indeed enable open relay by default, Exchange 2000 does not.

Nonetheless, the provided links to the articles will certainly explain the whole process - expecially Microsoft article Q310380.

by acattr

Contrary to Answer one, Exchange 2000 does not relay by default. It will only send to recipients domains listed in its default email policy. Exchange 5.5 does have open relay by default. I don't think your ASP would cause your clients server to be black listed. As long as your ASP program uses an email address that the exchange server is setup to send for, it is not relaying.

To check relaying connect to your server with telnet on port 25 over the internet(not from within the office).start
run
telnet mailserverNameorIP 25
helo domainname.com
mail from: spammer@domainname.com
rcpt to: billgates@microsoft.com

If it states relaying denied, your server doesnt relay, if it accepts the to billgates then you have a problem.
Listed below are articles on how to prevent mail relaying in Exchange 2000 and 5.5. You may want to make a relaying exception for your SQL servers IP address. The link will help you with that. PLease remove spaces from the link.

http://support.microsoft.com/default.aspx?scid=kb;en-us;Q310380

http://support.microsoft.com/default.aspx?scid=kb;en-us;Q315687

You can test a server for

by nsteere

Everyone had really good insight but #2 hit the mark with a great follow-up test! Thanks Again!!

by nsteere

Just for Info, The Application will produce about 300-900 emails a day listing our SQL Mail gateway email account as the sender. I dont want a blacklister to see that and say, "Damn, that guy sends out waay to much email, he must be a spammer". Thisscenario cannot happen if I set only the SQL IP as open relay?.

by joseph moore

SMTP mail servers all have this problem, of allowing themselves as being open relay servers. The RFC for SMTP did not address this issue, so that is why all of the SMTP servers have this "problem."
You see, open relay is not technically a deficiency of the mail servers. It never came up when the RFC was being written. It is only years later, when spam started, that the flaw in the logic of SMTP was pointed out.
For info on open relay, go here:
http://www.ordb.org/
You can look up on this site any IP address to see if it has been recorded as an open relay server. There are also links per SMTP server type on how to stop your server from being an open relay.
I think you should test your mail server like posted in Answer 2, and see if you can send spam. If you can hit port 25 on your mail server from an Internet address, and if your server does not block the MAIL FROM: command to only be mail from your e-mail domain, then yes, your server is open.

hope this helps

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