SLOW WAN WHEN EXCHANGE SERVER RUNNUNG

So what we are seeing (started about 48 hours ago)

When the exchange server is running we have high latency and packet loss to WAN. When exchange is not running we have full speeds.

We are running a Comcast pipe (22mbs x 5 mbs)
Setup is as follows:
1 Server 2008 Enterprise x86 (AD/DNS/DHCP/Print/Storage)
1 Server 2008 Enterprise x86_64 (AD/Exchange)
1 Server 2008 Enterprise x86_64 (AD/DNS/Terminal Services)

What we've done so far:
Replaced Modem
System updates
Checked for loopback cables
Verified we are not an open relay
Checked running services (nothing looks outta place, coulda missed something)
LVL 4
ckoningAsked:
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BusbarConnect With a Mentor Solutions ArchitectCommented:
no the maximum email's attachement size
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BusbarSolutions ArchitectCommented:
Hi,
what is your email limit, I believe that this load is generated by so many users sending large emails, can you confirm that
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ckoningAuthor Commented:
By Email Limit do you mean max connections?

It is set to 500 max connections with 100 per domain
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ckoningAuthor Commented:
Nope not the problem.

The max attachment size is 25MB but in the past we had unlimited and it was not a problem (when we were on Exchange 2003) ... the company only has about 25 employees, so not too much mail.

Also this seems to have nothing to do with mail load because it is the same all day and all night.
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ckoningAuthor Commented:
Also I should mention mail flow has been fine. We're getting mail moving around, and eveything on the LAN is fast. JUst when we try to go outside the LAN is it suuuuuper slow, with packet loss for everyone on the network.
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BusbarSolutions ArchitectCommented:
25 is big, if a user is sending 4-3 mails then you have 100 MB per user.
can you do packet sniffing and try to see the BW usage on the router
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ckoningAuthor Commented:
not too good with wireshark, what am I looking for?
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BusbarSolutions ArchitectCommented:
I am looking for what are the packets that Exchange is sending and causing the delay, Exchange only does SMTP and MAPI so if traffic comes from those sources then you have either a virus or a warm or a user who is sending so many emails
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ckoningAuthor Commented:
Sweet you are on the money. Lots and lots of SMTP traffic.

I didn't notice that the queue was all grouped by recipient domain (silly me!)

A very Tech stupid intern on the network sent out an email to a ton of people with a 20mb attachment (there was still about 200 reciepients over 50 domains). This was going for the last two days apparently, though I only heard about the slow internet this morning.
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ckoningAuthor Commented:
Got me looking in all the right places, thanks!
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BusbarSolutions ArchitectCommented:
you welcome, so happy that I helped
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