Re: Setup SMTP Filter

  • From: "Thomas W Shinder" <tshinder@xxxxxxxxxxxxxxxxxx>
  • To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
  • Date: Wed, 11 Jun 2003 23:52:32 -0500

Hi Muhammad,

Yes.

HTH<
Tom

Thomas W Shinder
www.isaserver.org/shinder 
ISA Server and Beyond: http://tinyurl.com/1jq1
Configuring ISA Server: http://tinyurl.com/1llp

 


-----Original Message-----
From: rizwan@xxxxxxxxxxx [mailto:rizwan@xxxxxxxxxxx] 
Sent: Wednesday, June 11, 2003 11:25 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] Re: Setup SMTP Filter


http://www.ISAserver.org




Dear All,

Please could anybody tell me that SMTP filter of ISA works with Domino
Mailserver Version 5.0.2.
Its urgent .

Awaiting your reply.

Kind regards,

Muhammad Rizwan Khalid
Asst. Manager M.I.S
------------------------------------------------------------------------
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Makkays                 Tel: +92 51 2822 075 (Ext.141)
Kulsum Plaza,         Fax: +92 51 2270 955
42 Jinnah Avenue,    Mobile: 0300 8503841
Islamabad,               E-Mail: rizwan@xxxxxxxxxxx
Pakistan.                 Web:  http://www.makkays.com
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---


 

                    "Jim

                    Harrison"            To:     "[ISAserver.org

                    <jim@isatools        Discussion List]"

                    .org>                <isalist@xxxxxxxxxxxxx>

                                         cc:

                    06/11/03             Subject:     [isalist] Re:
Setup 
                    08:13 PM             SMTP Filter

                    Please

                    respond to

                    "[ISAserver.o

                    rg Discussion

                    List]"

 

 




http://www.ISAserver.org


The thing is, the SMTP filter shouldn't reject non-command strings like
"500
XXXX command not recognized"
I'd still like to see that trace...

Unfortunately, the SMTP filter has no logging functionality.

 Jim Harrison
 MCP(NT4, W2K), A+, Network+, PCG
 http://www.microsoft.com/isaserver
 http://isaserver.org/Jim_Harrison
 http://isatools.org

 Read the help, books and articles!
----- Original Message -----
From: "William Robertson" <robertson.william@xxxxxxxxxxxxxx>
To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
Sent: Wednesday, June 11, 2003 07:59
Subject: [isalist] Re: Setup SMTP Filter


http://www.ISAserver.org


Hi Jim

I've done some more digging and discovered that the EHLO verb is an
ESMTP command and that's why all non-ESMTP enabled mail servers reply
with an Error 500 - Unknown Command. In this error these mail servers
"generalise" the original verb with placeholders (X) and thus say that
the verb XXXX was not recognised.

I tried creating a new XXXX SMTP verb the other day but I did not give
it a length of 71 (as is the case of HELO). After increasing the length
of the XXXX verb to 71, everything seems fine because now the firewall
allows the XXXX command to be passed through to my mail server, who then
switches over to the HELO command and then communication continues just
fine.

One last thing if you please, does ISA do any logging of all rejected
SMTP messages? I mean if I reject a specific domain/keyword/sender, does
ISA log this information anywhere?

Thanks
William R.


-----Original Message-----
From: Jim Harrison [mailto:jim@xxxxxxxxxxxx]
Sent: 11 June 2003 15:00 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] Re: Setup SMTP Filter

http://www.ISAserver.org


The quick answer is to add "XXXX" in the allowed list and give it the
same length as HELO.

The long answer is, "there's no such SMTP verb as XXXX".
Can you turn off the SMTP filter and get a trace of this converstation?
I've had some experience with the verb functions in the SMTP filter (can
we say AUTH?).

  Jim Harrison
  MCP(NT4, W2K), A+, Network+, PCG
  http://isaserver.org/Jim_Harrison/
  http://isatools.org
  Read the help / books / articles!



http://www.ISAserver.org


Hi there

I have now discovered the following on my mail server.
1) When it initiates a connection it issues an EHLO command as follows:
>>> EHLO columbus.co.za
2) I then get a reply from the receiving mail server as follows
500 Syntax error, command "XXXX columbus.co.za" unrecognized
3) Then my mail server tries another route as follows:
>>> HELO columbus.co.za
4) An then I get a valid reply:
250 madrid.acxgroup.com Hello columbus.co.za ([196.37.130.153]),
pleased to meet you

And then communication continues just fine. But when I enable the ISA
SMTP filter, I start getting the following alerts from my firewall:
ISA Server alert: An unknown SMTP command
XXXX MADRID.ACXGROUP.COM

So it would appear that the XXXX reply is somehow a "valid" SMTP
command/response, but how can I go about telling ISA to permit this
message through.

The thing is I can now quite happily just ignore these alerts, but then
my mail server is not going to get the XXXX response from the receiving
mail server, and thus my mail server won't know to try and use the HELO
command instead.

I can think that one resolution to this problem would be to force all
SMTP communication to begin with a HELO instead of an EHLO, but this
problem doesn't exist for all mail servers that I connect to. Which of
the 2 commands (EHLO and HELO) is the most universal and should be
accepted by ALL mail servers, regardless of the flavour (E.g. Exchange,
Sendmail etc etc)

Cheers
William R.



>>> MAIL From:<testcert-centre@xxxxxxxxxxxxxx>
250 testcert-centre@xxxxxxxxxxxxxxxxx Sender OK
>>> RCPT To:<codocs@xxxxxxxxxxxx>
250 codocs@xxxxxxxxxxxxxxx Recipient OK
>>> DATA


-----Original Message-----
From: Jim Harrison [mailto:jim@xxxxxxxxxxxx]
Sent: 03 June 2003 17:04 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] Re: Setup SMTP Filter

http://www.ISAserver.org


Are those commands actually "XXXX"?
If so, those aren't valid SMTP verbs and you then have two choices:
1. run your favorite packet tracer on the ISA external IP and watch for
this
event to fire.
    You can then watch the conversation up to that point to see what's
going
on.
2. contact the owners of those servers and ask them why they're sending
this
to you
If not, what are they?

 Jim Harrison
 MCP(NT4, W2K), A+, Network+, PCG
 http://www.microsoft.com/isaserver
 http://isaserver.org/Jim_Harrison
 http://isatools.org

 Read the help, books and articles!
----- Original Message -----
From: "William Robertson" <robertson.william@xxxxxxxxxxxxxx>
To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
Sent: Tuesday, June 03, 2003 07:20
Subject: [isalist] Re: Setup SMTP Filter


http://www.ISAserver.org


Hi Jim

After enabling the SMTP Filter and setting the NOOP length to 20 bytes,
I then started getting the following alerts from my Firewall:

ISA Server alert: An unknown SMTP command
XXXX ASTPROXY01.AST.CO.ZA
XXXX TCEN-UL-MAILSV01.TELKOM.CO.ZA
XXXX SMTP.LANTIC.NET
XXXX NS2.DHV.NL
XXXX MFCS002.SAMANCORCR.CO.ZA
XXXX JS000414.JOBSERVE.COM
XXXX AVEROMAR01.POVOAHOLDINGS.COM
etc
etc
etc

Do you perhaps know where I may start trying to figure out what exactly
these commands are that I need to enable? (BTW, I have a linux-based
sendmail server - no fancy schmancy exchange servers for me :(

Thanks
William R.

-----Original Message-----
From: Jim Harrison [mailto:jim@xxxxxxxxxxxx]
Sent: 02 June 2003 16:41 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] Re: Setup SMTP Filter

http://www.ISAserver.org


Generally, 20 is seen as a good upper limit for NOOP.
AUTH should be 1024, if you enable it.
Don't expect to screen HTML mail; the screener doesn't seem to like
them.

 Jim Harrison
 MCP(NT4, W2K), A+, Network+, PCG
 http://www.microsoft.com/isaserver
 http://isaserver.org/Jim_Harrison
 http://isatools.org

 Read the help, books and articles!
----- Original Message -----
From: "William Robertson" <robertson.william@xxxxxxxxxxxxxx>
To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
Sent: Monday, June 02, 2003 01:03
Subject: [isalist] Setup SMTP Filter


http://www.ISAserver.org


Hi there



My original installation of ISA Server excluded the setup of the SMTP
filter as I appeared to have problems with receiving mail etc. I have
now got some time on my hands ( yeah right.!) and would like to start
playing with it again.



I would like to know of any "out-the-box" tricks that I need to use to
get it working properly. I know for one thing that the default NOOP
value of 6 is apparently too small. Could someone please let me know
what a more acceptable NOOP setting is, as well as any other
variables/settings that I need to customise, or be on the lookout for.
Any reference to reading material to assist with the comprehension of
this topic would be a great asset.



Cheers

William R.



  _____


William Robertson

AST Mpumalanga


Systems House / Consultant: Software


Tel: 013-2472703 / 083 638 0354

   Fax: 013-2462236




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