<div>
Just what I was looking for. &nbsp;Thanks.
</div>


<div>
<div class="content wysiwyg-content">
Hi,<br />
<br />
I have a client who is using a bit of a strange setup. &nbsp;He receives mail directly via SMTP, it is first received by his sophos firewall SMTP proxy. &nbsp;The firewall calls out mail that is received to verify if the user exists before accepting the message. &nbsp;Messages are then scanned and forwarded to the mailsserver.<br />
<br />
Mail is sent, however, via a smart host of a different provider. &nbsp;<br />
(Long story - it has to do with their line issuing fixed IPs from a DHCP pool, so they are not fit for running a mailserver on because sent mail will not be accepted by many providers).<br />
This provider is then sending Mailer-Deamon replys to also non-existent senders (spammers) which results in blocking the account after a while.<br />
<br />
How do I train exchange to tell the firewall that an address does not exist so that it is rejected before transmission?<br />
<br />
To those who know Sophos: &nbsp;The firewall is AD-member, but setting it to check for existing adresses in AD results in each and every mail being rejected because it does not exist even though it does.<br />
<br />
Thanks,<br />
Ralph
</div>
</div>


Hi,

I have a client who is using a bit of a strange setup.  He receives mail directly via SMTP, it is first received by his sophos firewall SMTP proxy.  The firewall calls out mail that is received to verify if the user exists before accepting the message.  Messages are then scanned and forwarded to the mailsserver.

Mail is sent, however, via a smart host of a different provider.  
(Long story - it has to do with their line issuing fixed IPs from a DHCP pool, so they are not fit for running a mailserver on because sent mail will not be accepted by many providers).
This provider is then sending Mailer-Deamon replys to also non-existent senders (spammers) which results in blocking the account after a while.

How do I train exchange to tell the firewall that an address does not exist so that it is rejected before transmission?

To those who know Sophos:  The firewall is AD-member, but setting it to check for existing adresses in AD results in each and every mail being rejected because it does not exist even though it does.

Thanks,
Ralph

Exchange 2010:  Accepting mail to non-existent users

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.

Exchange

Various techniques are used to prevent email spam (unsolicited bulk email). No technique is a complete solution to the spam problem, and each has trade-offs between incorrectly rejecting legitimate email (false positives) vs. not rejecting all spam (false negatives) - and the associated costs in time and effort. Anti-spam techniques can be broken into four broad categories: those that require actions by individuals, those that can be automated by email administrators, those that can be automated by email senders and those employed by researchers and law enforcement officials.

AntiSpam

Sophos develops products for communication endpoint, encryption, network security, email security and mobile security as well as unified threat management. Products include hardware (or software virtual appliance) network firewalls including web browsing protection, AntiSpam filters and antivirus protection, encryption and data protection, web filter, antispam and mobile content and device management tools.