It will cause some inefficiencies in your transmission of data through the network/internet.

By the way, if the problem is in fact the NVidia NForce4 one that Thomas mentioned, you will likely see this error re-occur... it will be dependent on the message size being sent.

It is hard for me to believe the an MTU of 750 is proper for your setup.

You can figure out how to test it and optimize it for yourself using ping.

See the following for details:

http://www.dslreports.com/faq/5793
 

Hi - I have a small LAN, clients use pmail 441 to send and receive mail through a mail server.

We had a problem with the domain server yesterday, now fixed, and since then 2 of the users can't send mail, but all can receive it OK.

The error below happens if the SMTP is set to the mail server, or direct to the ISPs SMTP server. The mail gets bounced straight back saying "   *** TCP/IP error while processing job ***". I tried the suggestions from this thread: http://community.pmail.com/forums/thread/3722.aspx  to no avail - I would think the fact that other LAN users are OK must mean it's not an ISP issue

However most users are perfectly OK and the PCs affected haven't changed in any way so I am rather confused. Everything has been rebooted several times... any advice most appreciated!

regards

Rob 

 ========================================================

[*] Connection established to 192.168.0.2
>> 0073 220 server2k3 ESMTP WorkgroupMail 7.6.4 Tuesday, 22 April 2008 08:37:04
<< 0022 EHLO [192.168.0.216]
>> 0015 250-server2k3
>> 0016 250-AUTH LOGIN
>> 0016 250-AUTH=LOGIN
>> 0019 250 SIZE 20480000
<< 0041 MAIL FROM:<x@x> SIZE=9230
>> 0008 250 OK
<< 0033 RCPT TO:<y@y>
>> 0008 250 OK
<< 0006 DATA
>> 0022 354 Start Mail Input
7: Socket read error 2746.
 ========================================================

> Hi - I have a small LAN, clients use pmail 441 to send and receive
> mail through a mail server.
>
> We had a problem with the domain server yesterday, now fixed, and
> since then 2 of the users can't send mail, but all can receive it OK.
>
> The error below happens if the SMTP is set to the mail server, or
> direct to the ISPs SMTP server. The mail gets bounced straight back
> saying "   *** TCP/IP error while processing job ***". I tried the
> suggestions from this thread:
> http://community.pmail.com/forums/thread/3722.aspx  to no avail - I
> would think the fact that other LAN users are OK must mean it's not an
> ISP issue
>
> However most users are perfectly OK and the PCs affected haven't
> changed in any way so I am rather confused. Everything has been
> rebooted several times... any advice most appreciated!
>
> regards
>
> Rob
>
>  ========================================================
>
> Connection established to 192.168.0.2
> >> 0073 220 server2k3 ESMTP WorkgroupMail 7.6.4 Tuesday, 22 April 2008
> >> 08:37:04
> << 0022 EHLO [192.168.0.216]
> >> 0015 250-server2k3
> >> 0016 250-AUTH LOGIN
> >> 0016 250-AUTH=LOGIN
> >> 0019 250 SIZE 20480000
> << 0041 MAIL FROM:<x@x> SIZE=9230
> >> 0008 250 OK
> << 0033 RCPT TO:<y@y>
> >> 0008 250 OK
> << 0006 DATA
> >> 0022 354 Start Mail Input
> 7: Socket read error 2746.
>  ========================================================

I would first try increasing the TCP/IP timeout setting in Tools | Internet options | (Sending) SMTP to about 300 seconds to see if this fixes the problem.  If it does not then then the fix to the server might have caused a packet fragmentation problem.  The 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, do these computers, 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.

Hi - thanks for the reply.

I have changed my mind on what caused the problem, as I don't think I have sent email since upgrading to Vista SP1, and am sure this is the culprit. After all, if I send direct to smtp.isp.com then it isn't even going through the server...

Anyway I tried the network card fixes, and adjusting MTU (with command netsh interface ipv4 set subinterface "Local Area Connection" mtu=1430 store=persistent  (which is the vista way to adjust MTU) without improvement... I have an Intel chipset which had loads of options for Checksum Offload - I disabled all of them.. to no avail...

Any other ideas - in fact is anyone using Pmail with Vista SP1? 

Adjusted my MTU to 750 and it seems to be sending now.....

Any ideas what the downsides of making MTU much lower is?

-Rob