Hi,

I would like to know is it possible to configure in Sendmail to disable
the bounce back message to sender if the recipient is unknown "550
5.1.1 <recipient_address>... User unknown". Thanks.

"Simon" <Simon.SM.Li@gmail.com> writes:

> Hi,
>
> I would like to know is it possible to configure in Sendmail to disable
> the bounce back message to sender if the recipient is unknown "550
> 5.1.1 <recipient_address>... User unknown". Thanks.

None.

Generally bad idea. Will cause that mails to mistyped addresses go to
black hole.

Perhaps you should look problem from different light ?

/ Kari Hurtta

Simon wrote:
> Hi,
>
> I would like to know is it possible to configure in Sendmail to disable
> the bounce back message to sender if the recipient is unknown "550
> 5.1.1 <recipient_address>... User unknown". Thanks.

In the default configuration, sendmail does not "send a bounce message"
for unknown recipients. Rather, it rejects the mail and the connecting
hosts sends the message. This is ideal, since if the connecting host is
a spam zombie, no message is sent to a forged return address, but if
the message comes from a real MTA, that MTA will inform the sender of
the error.

If you have some kind of multi-stage process, and the first stage is
relaying all mail (not just mail to valid users), then the solution is
to inform the first stage of the list of valid users (perhaps using the
sendmail access or virtuser tables) rather than to disable bounces.

If you have something else in mind, you should detail your reasons.

Daniel Feenberg

Kari Hurtta wrote:
> "Simon" <Simon.SM.Li@gmail.com> writes:
>
>> Hi,
>>
>> I would like to know is it possible to configure in Sendmail to disable
>> the bounce back message to sender if the recipient is unknown "550
>> 5.1.1 <recipient_address>... User unknown". Thanks.
>
> None.
>
> Generally bad idea. Will cause that mails to mistyped addresses go to
> black hole.
>
> Perhaps you should look problem from different light ?
>
> / Kari Hurtta
I have the same problem. I receive over 1000 messages a day to
randomnames@mydomain.com. This number is growing weekly (I track them
before the logs get rotated). I've gone from a few hundred a week to
over 20,000 a week. On an impulse I wrote a script to look at the last
1000 lines in /var/log/maillog every 5 minutes and find any occurrenct
of "... User unknown".

> Oct 30 08:28:13 lazarus sendmail[6422]: k9UDSDd06422: <caninecommendatory@mydomain.com>... User unknown
> Oct 30 08:28:13 lazarus sendmail[6422]: k9UDSDd06422: from=<>, size=0, class=0, nrcpts=0, proto=SMTP, daemon=MTA, relay=sv203.lolipop.jp [202.181.96.40]

Since (on my server) the next line usually contains the sending party's
information, I pull the FQDN, IP Address, bogus email address (from
prior line) and the timestamp from the bounce. As there can be numerous
"User unknown" messages from that address I write the all to a MySQL
database then add new ones to a table which has a unique index defined
on the IP address. I take the IP Address from the unique table and add
it to IPTables blocking everything from that source.

I wanted to do this on another server I support but after looking at
/var/log/maillog it appears that this CentOS 4.x / Cyrus / Sendmail log
is very different from the Red Hat sendmail-8.11.6-27.72.