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Exchange 2010 Blocking External Mail IP Filter Only

Posted on 2014-02-16
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Last Modified: 2014-02-17
We have a client with an Exchange 2010 server which gets its email from 1 source - our external mail filter. It has worked for years fine but last week the EXCH system decided to start blocking the IP of the mail filter. Whilst it doesnt show up in the Blocked IP list - if I telnet to port 25 from any other system but the MX filter it is open. But when i telnet from the MX filter to port 25 it just shows nothing and then closes.

Every hour (appox) it opens up again (i can telnet from the MX filter fine) - and the MX filter can get some emails from the queue sent, but then blocks up again.

The system runs SP3. I have turned off all Anti Spam features of Exchange 2010, and also make change via the CLI -

Modify Default
-----------------
$a = Get-ThrottlingPolicy
$a | Set-ThrottlingPolicy -EwsMaxConcurrency 20
$a | Set-ThrottlingPolicy -EASMaxConcurrency 20
$a | Set-ThrottlingPolicy -MessageRateLimit 2000

Modify Rec Conn
------------------
Get-ReceiveConnector
Set ReceiveConnector "Windows SBS Internet Receive SERVER" -MaxInboundConnectionPercentagePerSource 30
-MessageRateLimit 2000
-MessageRateSource None

To no avail. When it is blocked i cant find anywhere in Exchange that tells me that it has blocked it - so I just dont know where to go from here. Ive routed email direct to them atm whcih is not the best option but at least gets them flowing.

So any thoughts ?
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Question by:jamesj21
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Accepted Solution

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Simon Butler (Sembee) earned 2000 total points
ID: 39864078
The behaviour you are seeing is not what I would expect to see if Exchange was blocking it.
If Exchange blocks it you get Service Unavailable being returned.
Therefore I would be looking at a third party tool, AV, Antispam etc.

Simon.
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Author Comment

by:jamesj21
ID: 39866165
Yep that was it - Kaspersky KES 10 was monitoring port25 and checking emails for Worms - which its not required to and I didnt know it did! So whitelisted the mail filter in KES and now fine. Also could see the blocks int the KES logs.

Thanks for the help.
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