Thank you every so much for solving the problem. It was indeed the issue of the NVIDIA NForce 4 chipset. I had to install the customisation utility in order to turn off "checksum offload" but doing so worked! I would never in a million years have thought of such an obscure thing without help, so many thanks again.

Martin

Ive been a PM user for many years and have had a successful installation on a 3 machine peer-to-peer Windows XP network. I had to re-install Windows on one machine. Having re-installed PM I can't send mail from that machine. I can receive mail normally and I can send mail when the body is only one word e.g. "test".  Add a bit of text in the body and the problem arises. PM hangs and returns an error message to the in-box:

On 17 Jul 2007 Pegasus Mail & Mercury - Automated Email <> wrote:

> Ive been a PM user for many years and have had a successful
> installation on a 3 machine peer-to-peer Windows XP network. I had
> to re-install Windows on one machine. Having re-installed PM I can't
> send mail from that machine. I can receive mail normally and I can
> send mail when the body is only one word e.g. "test".  Add a bit of
> text in the body and the problem arises. PM hangs and returns an
> error message to the in-box:
>
> *** TCP/IP error while processing job ***
>
> A network error has occurred while WinPMail attempted to send
>
> your message. This error could be caused by many conditions,
>
> including the following:
>
> * The remote host may have gone down.
>
> * Your network may have been broken or gone down.
>
> * You may have a configuration problem in your WINSOCK.DLL.
>
> * If running on a SLIP line, you may have experienced a
>
> timeout (increase the value in WinPMail's Network Config.
>
> Dialog), or the phone line may have gone down or suffered
>
> from excessive line noise.
>
> WinPMail will requeue your message and try again later.
>
>  I have checked that loading WSOCK32.DLL is set to "on demand". I
> can send the messages that hang on this machine, from either of the
> other two machines - which all use the same mailbox located
> physically on one of the other machines. The path to the mailbox is
> set on the other two to a network path, and there are several users.
> I suspect that PM can't find WSOCK.DLL but it is in the default
> place. The only other thing that is different about the problem PC
> is that it uses an ethernet-over-power connection but everything
> else works fine on this with a fast connection.
>
>  I have investigated everything I can, but can't find anything
> different about the problem PC. Any ideas please, anyone?
>
>  

A POP3/SMTP transmissions may fail if the MTU packet size is so large that a packet is fragmented.  In many cases the receiving system router blocks the receiving servers "packets fragmented" response to the sending system using "MTU Discovery".  These oversize packets are not accepted and so are resent.  This results in a timeout, generally at the end of the message transmission but it can be anywhere in the process.  You need to reduce the MTU size. Windows defaults to a 1500 MTU and many routers and DSL connections need 1492.  You might simply want to turn off the MTU Discovery operation.

You might want to get a copy of SG TCP Optimizer that I find quite handy.  http://www.speedguide.net/downloads.php  This little utility will allow you to test your MTU for maximum size without fragmentation against specific servers.  If will also make it easy to adjust the MTU.  

And finally, does this computer, by chance, happen to have an NVidia NForce 4 chipset on the motherboard?  If so, many other have had this exact problem, and it turned out to be an optimization setting for the built in NIC which caused the problems with packet fragmentation. Disabling the advanced optimization capability called "checksum offload" made all the problems of sending SMTP mail via WinPMail disappear.

Thanks for the reply. The NVIDIA cause sounds very likely to be the answer - I have not yet had a chance to try this out but will do so later in the week, as it does have that NIC, although it wasn't a problem previous to the re-installation of Wondows.

Thanks, Martin