Slow transmission speed of SMTP email

The Problem:
I have a number of machines (win2k & XP) running Office 2000 and Office 2003 that upon sending emails using SMTP only tranmit at 40KB/sec max whilst others transmit at full rate. (100Mb switched network).

Other Info:
I dont think its the emial server as most of the PC's can SMTP to it a full speed. On the PC's that are slow to TX to the email server i mapped a network drive and copied a 20MB file which only took a couple of seconds as you would expect. POPing from the email server on the same machines are fine too. It seems only SMTP outbound traffic is affected. On my Laptop which is one of the slow ones im running XP Pro, Office 2003 i tested sending a 20MB email to the server in both Outlook and Outlook Express and both of them exhibited slow SMTP transmissions.
Looking at the email server as it receives the SMTP packets its almost as if the client is throttling them as the throughput stays almost exactly at 40KB/s. I took my laptop home and put it on my home LAN and again it was slow to send SMTP mail.

My thinking so far is that it something on the client. Ive disabled the anti virus software, Thought it may have been activesync but one of the PC's in the office that is slow does not run Activesync.

Any ideas would be greatfully received !

Who is Participating?
sriwiConnect With a Mentor Commented:
TCP Received windows and MTU size, that is just a wild guess only.

have you check the dl speed using dsl speed test, and sometimes tweaking it as suggested on the website.

matt_loveAuthor Commented:
Thanks for the suggestions, I will check these out tomorrow when im back in the office.
Now you mention about MTU's i will see if the Cisco VPN client resides on only these affected computers, its certainly on my laptop....
The email server is on my LAN so in this instance there is no DSL.
in your case here, the cisco maybe slow it down, do you have a rate limit set up on your router, so that the email traffic doesn't kill of the other important traffic ?
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matt_loveAuthor Commented:
I checked the routers and cant see any throttleing, i also put my laptop on the Cisco Switch the Email server is connected to, gave myself  an ip address in the same subnet and still slow..
I have a machine on the test bench that im slowly adding software to, to see when it breaks. Currently just about to install vpn client. Fun !
are you running on linksys wireless ? on the laptop ?

also just wondering, what setup have you got over there ?

you got dhcp ?? which dns you point to ? and what is internet speed ? what connection type ?
matt_loveAuthor Commented:
No wireless at these sites.

DHCP from W2K Server, no local DNS (which i think is not helping), machines point to proxy or ISP's DNS. Internet conection is via Cisco 837's on a 2Mb ADSL. All the machines in question are on the same subnet and are connected using Cisco 2950 switches. The remote side of the VPN uses the same, Cisco 837's.

in a week or 2 the perimeter of the network will change to using PIX 515's and use the 837 simply as ADSL interface routers.

thanks for your discussion and help. :o)
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