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Exchange 2007 - Failure DSNs Total

Posted on 2013-01-14
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Last Modified: 2013-03-09
Hello,

I observed that in my Hub transport server (exchange 2007)the Failure DSNs Total  valuse is more than 32000. Is that normal or any issues?

I didnot see any error in events.

If it is the issue please some one help to decrease this value.
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Question by:Haribaskaran
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Expert Comment

by:ArneLovius
ID: 38778484
Without knowing the content of the Delivery Status Notification messages, but presuming that they are "failures" it is difficult to know the cause

Are they for internal or external addresses ?

Is your server running as an open relay ?

Are you filtering inbound email against valid email addresses ?
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Expert Comment

by:Manpreet SIngh Khatra
ID: 38779051
Just to add to Arne

Perfect point of Open relay ....
Check with EXBPA if that reports any errors ..
How many servers and hope you have AV and ensured no server is affected ?

- Rancy
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Author Comment

by:Haribaskaran
ID: 38779117
Hello ArneLovius,

It is not opened relay we are relaying the mails via forefront solutions.
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Expert Comment

by:ArneLovius
ID: 38779185
the other three questions in my post are also relevant

as per Rancy, running the ExBPA is an excellent suggestion.

Running ForeFront would make is harder to be an open relay, but certainly not impossible...
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Author Comment

by:Haribaskaran
ID: 38779213
Ok Let me  run the EXBPA and share the result.
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Author Comment

by:Haribaskaran
ID: 38779623
Hi I ran the EXBPA and I didn't see any errors reated to this. I have attached the screen shot of that.
Test.jpg
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Expert Comment

by:ArneLovius
ID: 38779743
Are they for internal or external addresses ?

Are you filtering inbound email against valid email addresses ?
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Author Comment

by:Haribaskaran
ID: 38779900
That is for External. yes Inbound mail filtering enabled against valid email addresses.
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Expert Comment

by:ArneLovius
ID: 38779980
in which case, time to do some research.

open the most recent DSN and note down who it is To:
now use the tracking log to see if you can find the original.
If you can find the original, this will tell you who it was To:

I'm going to guess that either the mail filter for valid addresses is not working, or that your outbound gateway is not allowing you to send DSN messages.
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Author Comment

by:Haribaskaran
ID: 38780021
OK Let me check on that.
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Expert Comment

by:Manpreet SIngh Khatra
ID: 38781485
Arne i guess we should place Recipient and Sender Filtering as well ?

- Rancy
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Accepted Solution

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ArneLovius earned 500 total points
ID: 38782047
I always enable recipient filtering on the mail gateway, whether this is n Exchange HT role, Edge Transport or 3rd party mail gateway, this is to ensure that DSN failure emails are NOT sent for invalid email addresses, DSN failures should be sent by the sending mail server back to the sender.

If recipient filtering is not enabled it can lead to a build up of DSN failure messages as described, these can also be used in an "amplification attacks" where a zero sized email from a spoofed address turns into a DSN failure to the attacked address.

I only use sender filtering to block known "spam" or "harassment" email addresses.
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Author Comment

by:Haribaskaran
ID: 38842390
I resolved this issue, thanks for all response.
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Expert Comment

by:ArneLovius
ID: 38843007
how did you resolve it ?
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