Stop accepting connections for sending e-mail from users not having a mailbox

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N

Nezos



Greetings,

i have an exchange server 2010 used for receiving and sending e-mail from/to the internet. My server then was found out by spammers and they started sending massive e-mails to other people outside our domain. I stopped this by setting a filter that checks the sender and if the sender is not on the list then it deletes the message. By this way though, the server received the message and then deleted it, but never spammed other mail servers on the internet.

Is there a way to stop the attack in an earlier stage, before the server saves the message? I mean there is a lot of traffic generated by this, can i disconnect them without receiving the message?

Or do you suggest another approach?

Thank you all
 
N

Nezos



Thanks Leif for your response but it doesn't help me.

I want to be able to exchange e-mails with users outside the domain of my server. So in some way it must relay.

There must be a way to stop the spammers from giving the server the message that they want to send to other mail servers, e.g. yahoo, hotmail, etc.

Am i missing something?
 
L

Leif Pedersen [MVP]



Hi,

The problem is on your receive connector where you are accepting mails to any recipients (and thereby allowing external users to send mails to other external users). External users sending mails to users on your server is not relaying.

So only if you have application servers sending mails through your exchange servers it must be configured to relay - but here you can restrict by IP addresses of your application servers.

Leif
 
N

Nezos



In the Server Configuration -> Hub Transport-> Receive connectors , i have 2 connectors "Client" and "Default".

The client has checked for Authentication : "TLS" and "Basic Authentication after TSL" and for Permission: "Exchange Users" and "Exchange servers"

The default has checked for Authentication: "TLS" and for Permissions: "Anonymous users, Exchange users and servers and Legacy Exchange Servers"

Where should i make changes?
 
L

Leif Pedersen [MVP]



Hi,

It must be on the default connector that there are some extended permissions set ( -ExtendedRights "Ms-Exch-SMTP-Accept-Any-Recipient"). These should be removed

Leif
 
N

Nezos



I though the previous post was a solution to my problem since i was checking the Message Tracking tool of the Exchange Server.

The i tried to check the server using: http://www.checkor.com/

220 MYADDRESS Microsoft ESMTP MAIL Service ready at Thu, 16 Dec 2010 15:27:29 +0200
HELO ortest.checkor.com
250 MYADDRESS Hello [204.16.252.112]
RSET
250 2.0.0 Resetting
MAIL FROM: test@checkor.com
250 2.1.0 Sender OK
RCPT TO: test1@checkor.com
Test Failed, 250 2.1.5 Recipient OK

It seems that the connection is still done, even though the RCPT TO: is different than that of the users on my server. I tried also with Putty and the server received the mail, although it got rejected by Content Filtering.

Any other solution to stop the connection at the RCPT level?
 
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