Outbound OK, inbound timeout errors

Anthony · Joined: 05 Aug 2007 Posts: 1

Our mailserver connects to a third party barracuda device. They receive all
our mail and also are a pass-through on our mail delivery. Outbound mail is
delivered fine, but when their machine attempts to connect to us for inbound,
the connections sometimes time out (ACK, SYN timeout) after :30 seconds.

I have gone over the firewall settings and there is nothing that is
preventing this. All was working 100% until last Friday. Over the weekend all
was well, then Monday it started again around 10 am local. It stopped at
around 6 pm. All regular internet traffic is smooth, no hickups (7 T1's).

I think it's a DoS attack on port 25, but I may be incorrect. The times that
the attack are happening coincide with business hours. What can I check
within Exchange to make sure it's not Exchange causing this problem? I have
run a packet monitor, and it shows connections are flowing, but I didn't do
this till after 6pm. I have over 100 users receiving email, and it's causing
problems. We can't have our network down.
--
Anthony

Archived from group: microsoft>public>exchange>connectivity

John Oliver, Jr. [MVP] · Joined: 05 Aug 2007 Posts: 823

Download Exchange Troubleshooting Assistant,

http://technet.microsoft.com/en-us/exchange/bb288481.aspx

Verify the Barracuda Logs to insure its not the cause.

--
John Oliver, Jr
MCSE, MCT, CCNA
Exchange MVP 2008
Microsoft Certified Partner

"Anthony" wrote in message @microsoft.com...
> Our mailserver connects to a third party barracuda device. They receive
> all
> our mail and also are a pass-through on our mail delivery. Outbound mail
> is
> delivered fine, but when their machine attempts to connect to us for
> inbound,
> the connections sometimes time out (ACK, SYN timeout) after :30 seconds.
>
> I have gone over the firewall settings and there is nothing that is
> preventing this. All was working 100% until last Friday. Over the weekend
> all
> was well, then Monday it started again around 10 am local. It stopped at
> around 6 pm. All regular internet traffic is smooth, no hickups (7 T1's).
>
> I think it's a DoS attack on port 25, but I may be incorrect. The times
> that
> the attack are happening coincide with business hours. What can I check
> within Exchange to make sure it's not Exchange causing this problem? I
> have
> run a packet monitor, and it shows connections are flowing, but I didn't
> do
> this till after 6pm. I have over 100 users receiving email, and it's
> causing
> problems. We can't have our network down.
> --
> Anthony

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