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Some Inbound SMTP denied - 24.Jul.2008 9:22:45 AM

jlt70

Posts: 16
Joined: 27.May2008
Status: offline

I seem to have the same problem as a lot of people out there, only I can't find any trace of an answer:

ISA 2006 is behind a NAT router (for connection failover) and is publishing Exchange for inbound SMTP using the SMTP Server wizard. Most email comes in OK with two live logs:

Client IP     ExchangeIP    Port25    SMTP Server   Initiated Connection
Client IP     ExchangeIP    Port25    SMTP Server   Closed Connection

HOWEVER, email from some people shows the following additional log:

Client IP     ISA IP           Port25    SMTP              Denied Connection

And the email is blocked (SMTP logs just show a 'QUIT'). Why isn't the SMTP server rule letting this through to the Exchange server too?

The only hint of an answer I can find online is 'It was an MTU issue' - but I'm not convinced. Please help if you have any ideas I'm out of ideas...

Thanks Jon

< Message edited by jlt70 -- 8.Aug.2008 4:25:06 AM >

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RE: Some Inbound SMTP denied - Please help! - 1.Aug.2008 5:21:06 AM

jlt70

Posts: 16
Joined: 27.May2008
Status: offline

Update:
I've removed the NAT router so ISA is now in text-book config with a real IP address on the external adapter. Same problem. What can it be? I really could do with some help!

(in reply to jlt70)

Post #: 2

RE: Some Inbound SMTP denied - Please help! - 5.Aug.2008 9:42:56 AM

jlt70

Posts: 16
Joined: 27.May2008
Status: offline

After much research things are a little clearer:

The only confirmed case of genuine email (i.e. not spam) being blocked was due to the SMTP filter having the default (incorrect) maximum length for the NOOP command http://support.microsoft.com/?kbid=312213.

Lots of other email is still comming in showing FWX_E_CONNECTION_KILLED (or FWX_E_ABORTIVE_SHUTDOWN without the SMTP filter in place) followed in some cases by FWX_E_TCP_NOT_SYN_PACKET_DROPPED. But I will make this the subject of a new post since I'm on my own here.

(in reply to jlt70)

Post #: 3

RE: Some Inbound SMTP denied - Please help! - 8.Aug.2008 4:26:10 AM