[lug] Sending e-Mail under Linux

[Franklin Bowen]

I assumed I was not an open relay because my internet connection is through 
a Cisco 678 DSL modem (which is a router) with NAT turned on.  However, you 
know what they say about assuming...  :-)  So I found a URL that allows one 
to actually test whether they are an open relay:

http://www.abuse.net/relay.html

I don't have an account so I did the anonymous test which came up 
negative.  From what I read on their page that is definitive.  If you get a 
positive test as anonymous, it is still possible that you are NOT an open 
relay and need to get an account or find another test to find out for sure.


At 08:46 AM 8/29/2002 -0600, you wrote:
>John:
>
> > One final question - I've heard that spammers could use my computer
> > as a mail-relay (something about telnetting via port 25?).  How can I
> > detect and/or prevent that from happening?  Or is that even a concern
> > for a home user?
>
>Open relaying is a concern for *anyone* who's got a direct Internet
>connection, home users included.  Many spammers employ portscanners
>that sweep over a range of IP addresses and find servers whose SMTP
>port (25) is open.  Then they relay their mail off it.
>
>If you have a static IP, you're a juicier target than someone whose IP
>changes every time they go online.
>
>Three solutions present themselves, in increasing complexity:
>
>1) Disable Sendmail.  This will close port 25, and force you to use your
>ISP to send your mail.  All ISPs provide a mail relay for their users,
>and AT&T should be no exception.
>
>2) Use a firewall.  Block port 25 (and nearly everything else, in fact).
>This will allow you to still use Sendmail locally to send your
>messages-- although, as Warren pointed out, some mail servers will
>refuse mail from "localhost".
>
>3) Use selective relaying, so you define which IPs can use port 25 to
>send mail.  Obviously you'd allow yourself (127.0.0.1), and potentially
>allow your friends (with their static IPs) to relay off you.  Not
>recommended, but possible.
>
>HTH,
>Jeff
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--
Franklin Bowen (Franklin at Bowen.net)
http://Franklin.Bowen.net