R: [OT] How to avoid Backscatter in Sendmail

[Steve Freegard]

On 21/04/10 14:50, Marcello Anderlini wrote:
> No my system is a Linux Centos with sendmail

If the mailboxes are for local UNIX users then generating backscatter 
for unknown users is impossible unless you are using something like 
Cyrus (which requires a plug-in to verify users).

I've just checked and unless I'm missing something:

smf at smf-laptop:~$ host -t MX database.it
database.it mail is handled by 10 netra2.database.it.

smf at smf-laptop:~$ host netra2.database.it
netra2.database.it has address 83.216.185.70

smf at smf-laptop:~$ host 70.185.216.83.ips.backscatterer.org
Host 70.185.216.83.ips.backscatterer.org not found: 3(NXDOMAIN)

^^^ Shows that you are not listed

Also I checked:

smf at smf-laptop:~$ telnet netra2.database.it 25
Trying 83.216.185.70...
Connected to netra2.database.it (83.216.185.70).
Escape character is '^]'.
220 netra.database.it ESMTP Sendmail 8.13.1/8.13.1; Wed, 21 Apr 2010 
16:07:36 +0200
EHLO foo
250-netra.database.it Hello 
74-93-209-150-WashingtonDC.hfc.comcastbusiness.net [74.93.209.150], 
pleased to meet you
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-8BITMIME
250-SIZE
250-DSN
250-AUTH DIGEST-MD5 CRAM-MD5 LOGIN PLAIN
250-DELIVERBY
250 HELP
MAIL FROM:<>
250 2.1.0 <>... Sender ok
RCPT TO:<sldjfskldjfslkdfjs at database.it>
550 5.1.1 <sldjfskldjfslkdfjs at database.it>... User unknown
QUIT
221 2.0.0 netra.database.it closing connection
Connection closed by foreign host.

^^^ Shows that you are correctly rejecting unknown users at the SMTP stage.

So I can't see any problems at all.

Regards,
Steve.