Slow transmission speed of SMTP email

Posted on 2005-04-06
Last Modified: 2012-06-27
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 !

Question by:matt_love
    LVL 4

    Accepted Solution

    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.


    Author Comment

    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.
    LVL 4

    Expert Comment

    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 ?

    Author Comment

    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 !
    LVL 4

    Expert Comment

    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 ?

    Author Comment

    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)

    Write Comment

    Please enter a first name

    Please enter a last name

    We will never share this with anyone.

    Featured Post

    How to run any project with ease

    Manage projects of all sizes how you want. Great for personal to-do lists, project milestones, team priorities and launch plans.
    - Combine task lists, docs, spreadsheets, and chat in one
    - View and edit from mobile/offline
    - Cut down on emails

    Let’s list some of the technologies that enable smooth teleworking. 
    If your business is like most, chances are you still need to maintain a fax infrastructure for your staff. It’s hard to believe that a communication technology that was thriving in the mid-80s could still be an essential part of your team’s modern I…
    Get a first impression of how PRTG looks and learn how it works.   This video is a short introduction to PRTG, as an initial overview or as a quick start for new PRTG users.
    This video gives you a great overview about bandwidth monitoring with SNMP and WMI with our network monitoring solution PRTG Network Monitor ( If you're looking for how to monitor bandwidth using netflow or packet s…

    779 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    16 Experts available now in Live!

    Get 1:1 Help Now