RE: Unresolved recipients don't get filtered ?

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Good Day Jenny,

Thank you for help.

There two MX records: first one pointing to the SBS static IP, second to
beanfield.com which is also authoritative for the mycompany.com SMTP domain.
The second mail server beanfield.com which I belive is using VPOPmail, is
responsible for generating NDR, being at the end of the chain.
http://support.microsoft.com/kb/321721/
Some employees don't have an account on the SBS server, however they have an
email address @mycompany.com residing on beanfield com.
When an email comes in to SBS if the address is not found in Active
Directories, Exchange will forward that email to Beanfield.com as uresolved
recipient, so external users can retrieve their emails.
There's a bit more work with this setup as 3 sets of accounts have to be
maintained ( SBS, POP3 connector, and WebMail on Beanfield ), but if there's
a problem with the SBS or Internet, the users can use webmail to access their
emails, then when SBS is back on line it will pull all the emails with the
pop3 connector.// ++ saving in licenses for the external users...
The growing problem is with invalid addresses, due to spoofed domain, that
go to the second server, or trying as sometimes get stuck in the Exchange
Queue.
What are your thaughts working with this setup, and what would be a better
way of dealing with spam?

Your help is much appreciated.
Daniel

""Jenny wu [MSFT]"" wrote:

Hi Daniel,

Thanks for using the SBS newsgroup.

To answer your second question:

SenderID (http://www.microsoft.com/senderid) is the e-mail authentication
framework that targets one of the most common security issues in the world
of SMTP message transfer, which is spoofing. In short Sender ID allows
administrators of an e-mail domain to protect the identity of this e-mail
domain by registering the special DNS record, also called SPF record, that
lists the hosts (IP addresses, names, etc) that are authorized to send
e-mail from that domain. For example the SPF record for @microsoft.com
e-mail domain lists about 20 authorized hosts. You can pre-view the record
by doing "nslookup -q=TXT Microsoft.com" and then "nslookup -q=TXT
_spf.microsoft.com".

So Exchange 2003 SP2 allows to query Internet DNS for SenderID/SPF records
for the given domain mentioned as the sender domain in an e-mail message
and then, depending on the result of that check, take appropriate actions
on that message,. The action could range from blocking the message at the
protocol level (for example when SenderID check returns the "Failed"
status) or passing the message to the next layer of filtering such as
Intelligent Message Filter which takes the SenderID check result into
account when making its anti-spam analysis decisions.

So the Send ID does not filter unresolved recipient emails. If we select
the Reject option in the Sender ID Filtering, the recipient will not
receive the specific message that failed the Sender ID verification and the
NDR notification will be sent to the sender directly.

For more detailed information about how to configure the Sender ID
Filtering, please refer to the following articles:

Sender ID Home Page
http://www.microsoft.com/mscorp/safety/technologies/senderid/default.mspx

Sender ID Framework SPF Record Wizard
http://www.anti-spamtools.org/SenderIDEmailPolicyTool/Default.aspx

Sender ID
http://blogs.technet.com/exchange/archive/2005/10/13/412487.aspx

Before we go further to your first question, please kindly help me collect
some information to isolate the issue.

1. What is your network topology? Please describe more detail about your
network structure for analyze the issue.

2. What is the meaning of the sentence "We need that as some remote users
don't have a domain account but they need an email address @mycompany.com.
"? How you implement the function that one user account has not domain
account but has domain email address?

3. What is the "the second server"? Is it exchange server or other servers?
Where it locates in network? What is the relationship between the second
server and exchange server or SBS server box?

I appreciate your time! I am happy to be of assistance to you and look
forward to your reply.

Have a nice day!

Sincerely,

Jenny Wu
Microsoft CSS Online Newsgroup Support
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Thread-Topic: Unresolved recipients don't get filtered ?
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From: =?Utf-8?B?RGFuaWVs?= <Daniel@xxxxxxxxxxxxxxxxxxxxxxxxx>
Subject: Unresolved recipients don't get filtered ?
Date: Mon, 6 Feb 2006 17:03:27 -0800
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Hello Everybody,

There are 3 filter mechanisms against spam: Message Screener provided by
ISA2k4, IMF by Exchange and TrendMicro CSM ver3, however the last 2
filters
don't seem to filter emails sent to a second mail server as unresolved
recipients. We need that as some remote users don't have a domain account
but
they need an email address @mycompany.com. The main problem is that the
second server rejects some emails and the queue can get very large on
Exchange Server, which has to be cleaned up regularly.
Have I missed a setting or is it normal that IMF and Trend don't filter
emails redirected to another mail server?
The other question I have is Sender ID going to filter these unresolved
recipient emails?

Your input is much appreciated.
Daniel



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