Re: Sendmail question

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Date: Mon, 14 Feb 2005 10:53:26 -0500
To: freebsd-isp@freebsd.org

Deep in the forest in the dark of night on Mon, Feb 14, 2005 at 07:20
with a cackle and an evil grin Suporte Matik cast another eye of
newt into the brew and chanted:

> On Monday 14 February 2005 01:33, Noah Davidson wrote:
>
> > Yes I have the mailertab working as expected. The issue is
> > that all rejected mail from the exchange server is bouncing
> > back and a copy is sent to the root user's mailbox. This
> > bounced mail is filling up the root mailbox. Is there anyway
> > to not have the bounced mail go to the root mailbox?

> yes! do not send them to root ;)

> you must have something misconfigured because the mailgatway
> root should not get anything back from your other mailserver
> because it is not the sender. I do not know about your exchange
> server but if it bounce mail it should go back to the sender MTA
> and not to the mailgateway - but if so you have something wrong
> IMO

We had a client who decided they'd rather have an in-house email
server than use ours. We handled their DNS and hosted their
web-services also

So I repointed the MX records to their machine.

A while later I was greeted by a flood of messages in the root mbox
as the MS machine was reejecting every piece of mail that was not
for a local user and returning them to the sender.

Since most messages of this type were spam sent from bogus
addresses they were bounced back from the forged address/domain.

The solution was simple. I turned off their mail service until
they reconfigured their mail server to behave in a more appropriate
manner.

We were also running as their secondary MX and that was removed at
that time.

They had two choices - don't abuse our services or find another
ISP.

> > Thanks
> > Noah
> >
> > ________________________________
> >
> > From: owner-freebsd-isp@freebsd.org on behalf of Suporte Matik
> > Sent: Sun 2/13/2005 6:11 PM
> > To: freebsd-isp@freebsd.org
> > Subject: Re: Sendmail question
> >
> > On Sunday 13 February 2005 23:56, Noah Davidson wrote:
> > > This is a backup mail server. The primary mail server is an Exchange
> > > 2003 server. So when mail is sent to invaliduser@bdomain.com then this
> > > server sends the mail to the exchange server that is responsible for
> > > handling the
> >
> > you wrote:
> > > > > I have set up a new FreeBSD box as mainly a backup mail server,
> > > > > although it is primary for a couple of domains. It is running
> > > > > sendmail 8.13.3 and it works fine, except for all the spam that
> >
> > but sorry for not understanding your strange crypt ...
> >
> > > mail for domain.com. Since the user does not exist it bounces the mail.
> > > Then the root alias gets a copy of the bounced mail. Is there any way to
> > > prevent this from happening? This server should just queue the mail for
> > > the exchange server until the exchange server is available.
> >
> > but anyway you may use /etc/mailertable and put a line like this for each
> > domain you forward and there should no additional mail processing until the
> > msg timed out conforming your sendmail.cf settings
> >
> > .domain.com smtp:windots.com.br
> >
> > aditional you need add to your local-host-names the host name as used in
> > the domains MX record
> >
> > > Thanks
> > > Noah Davidson
> > >
> > > ________________________________
> > >
> > > From: owner-freebsd-isp@freebsd.org on behalf of Bill Vermillion
> > > Sent: Sun 2/13/2005 5:42 PM
> > > To: freebsd-isp@freebsd.org
> > > Subject: Re: Sendmail question
> > >
> > >
> > >
> > > I know you'll find this hard to believe, but on Sun, Feb 13, 2005 at
> > > 23:13 ,
> > >
> > > Suporte Matik actually admitted to saying:
> > > > On Sunday 13 February 2005 22:46, Noah Davidson wrote:
> > > > > The only problem with that approach is that this is a back up
> > > > > server and the users may not be able to know of all of the
> > > > > users. Is there any way to not have all of these bounced mail
> > > > > go to the postmaster / root account.
> > > >
> > > > sendmail should reject mail for nonexistent users by default
> > > > and not forward to root unless you have any strange alias for
> > > > all but you say bounced mail what confuses me a little bit, but
> > > > anyway, isn't it that your systema accounts are exploited by
> > > > the spammers ? so if having 10 domains you may get 10 spams for
> > > > tty in your root mailbox, to prevent you may try this in your
> > > > access:
> > > >
> > > > tty@ ERROR:"4.2.2:450 No such user here."
> > > >
> > > > and so on for each systema account and rebuild the access.db and
> > > > probably your headache goes away
> > >
> > > The problem I have is that when mail is bounced back mail from
> > > spammers often comes from forged addresses and I get emails
> > > from the far site indicating there are unknown users.
> > >
> > > So I find routing noexistant users to /dev/null is more productive.
> > > While it's not exactly the best way to do it, there are so many
> > > bogus addresses sending mail I haven't found a good alternative.
> > >
> > > One site we handle has one of those strong standalone names that
> > > don't require any advertising to come up #1 on google or msn and
> > > when it finally hit 300,000 spams/day for that one domain I took
> > > out the MX records.
> > >
> > > I use the access.db for blocking known places and I won't send
> > > anything back at all - I used the DISCARD verb as sending messages
> > > back does nothing but generate more traffic.
> > >
> > > > > ________________________________
> > > > >
> > > > > From: Bill Vermillion [mailto:bv@wjv.com]
> > > > > Sent: Sun 2/13/2005 2:30 PM
> > > > > To: Noah Davidson
> > > > > Cc: FreeBSD-ISP List
> > > > > Subject: Re: Sendmail question
> > > > >
> > > > >
> > > > >
> > > > > Ashes to ashes, and DOS to DOS Noah Davidson was heard to say
> > > > >
> > > > > on or about Sun, Feb 13, 2005 at 14:10 :
> > > > > > I have set up a new FreeBSD box as mainly a backup mail server,
> > > > > > although it is primary for a couple of domains. It is running
> > > > > > sendmail 8.13.3 and it works fine, except for all the spam that
> > > > > > is being sent to it to bad email addresses. I have aliased
> > > > > > the root account to an email group on another server so that
> > > > > > someone reads the root mail. The problem is that all the mail
> > > > > > that spammers are sending to address that do not exist get
> > > > > > bounced and the root account a notification (I believe it
> > > > > > is the postmaster alias which is aliased to root). Is there
> > > > > > any way to not have these notifications sent out. They are
> > > > > > filling up the mail boxes. I just want the return to sender, but
> > > > > > not to the root / postmaster as well. I have tried using the
> > > > > > confCOPY_ERRORS_TO in my .mc file, but that just sends it to an
> > > > > > additional account as well.
> > > > >
> > > > > Making assumptions that your sendmail is receiving bogus mail
> > > > > for accounts that you have sendmail receive here is approach you
> > > > > can take.
> > > > >
> > > > > Assume you have domains a.com b.com and c.com and your
> > > > > local-host-names has those.
> > > > >
> > > > > Then you need to find out what users you have for each domain
> > > > >
> > > > > If you have curly larry and moe on a.com and no one else, then you
> > > > > can build a virtualusrtable that looks like this.
> > > > >
> > > > > curly@a.com curly
> > > > > larry@a.com larry
> > > > > moe@a.com moe
> > > > > @a.com nouser
> > > > >
> > > > > And the accnount 'nouser' will be in your /etc/mail/aliases
> > > > > file and will look like this:
> > > > >
> > > > > nouser: /dev/null
> > > > >
> > > > > Run make in /etc/mail to create virtusertable.db and aliases.db
> > > > > and that should get rid of the bogus names going to root.
> > > > >
> > > > > I find the virtualusertable to be quite handy for elminating a lot
> > > > > of junk. It will only be a problem if you have a large user
> > > > > base or lots of domains.
> > > > >
> > > > > Bill
> > > > > --
> > > > > Bill Vermillion - bv @ wjv . com
> > > > >
> > > > >
> > > > > _______________________________________________
> > > > > freebsd-isp@freebsd.org mailing list
> > > > > http://lists.freebsd.org/mailman/listinfo/freebsd-isp
> > > > > To unsubscribe, send any mail to
> > > > > "freebsd-isp-unsubscribe@freebsd.org"
> > > >
> > > > --
> > > >
> > > >
> > > > Infomatik
> > > > implementamos asas na sua rede.
> > > > (18)3551.3591 (18)8112.7007
> > > > _______________________________________________________
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> > >
> > > --
> > > Bill Vermillion - bv @ wjv . com
> > > _______________________________________________
> > > freebsd-isp@freebsd.org mailing list
> > > http://lists.freebsd.org/mailman/listinfo/freebsd-isp
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> > >
> > >
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> >
> > --
> >
> >
> > Infomatik
> > implementamos asas na sua rede.
> > (18)3551.3591 (18)8112.7007
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>
> --
>
>
> Infomatik
> implementamos asas na sua rede.
> (18)3551.3591 (18)8112.7007
> _______________________________________________________
> Participe na lista de seguran?a,
> recebendo as mais importantes not?cias na hora
> Entre em http://info.matik.com.br e participe.
> _______________________________________________________
> Mensagens sem assinatura GPG n?o s?o nossas.
> Messages without GPG signature are not from us.
> _______________________________________________________

-- 
Bill Vermillion - bv @ wjv . com
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