[Dshield] Exchange Open Relay
pandry at wolverinefreight.ca
Wed Feb 22 20:14:10 GMT 2006
Arthur Neville wrote:
> I posted before about how my domain is being whacked by Spam and how some users are contsantly getting hammered
> I checked our public facing email server to see if its an Open Relay....
> I was able to telnet into 25 and send mail from the outside hmmmmm
> We use an intranet and within that intranet there is windows integrated authenticated, we are using Outlook Web Access and Outlook Mobile Access for our smartphones
> I heard one of the WinAdmins speak about needing SMTP to communicate between the servers and that there are no open relay's.... duhhhh guess what
> I went to one of the sites that checks the site to see if it is on any DNSBNL's and voila we are on about 50 dnsbl's on the net.....
> Does that mean we have someone using our server as an open relay ???
> Or we have someone who has some bots on his box or boxes....
> In any event....thats the scoopla, I am well versed in the art of reading so if you have some links or info that would be helpful that would be kewl
> Brings words and photos together (easily) with
> PhotoMail - it's free and works with Yahoo! Mail.
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Which version of Exchange? Exchange 5.5 is an open relay by design, and
you need to edit a registry key to turn it off. Exchange 2000 is, iirc,
secured against it.
Exchange, even properly secured, will fail some of the open relay tests,
due to the handling of the inbound mail. It accepts pretty much all
mail, then will decide if it needs to be discarded. If you test your
mailserver using some of the online open relay tests, be aware of this.
The spambots are pretty easy to choke out at the firewall. Just deny
all traffic destined to the internet on port 25 from everything but your
mail server. Web scripts are notorious for e-mail relay, and any
contact forms should be audited. Anti-virus and anti-adware software
will find any rogue clients.
Finally, a big "mea culpa" to all of the blacklists, coupled with time
and good behavior, will get you off the lists.
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