Networking/SMTP issue

[rhys]

I rarely tread here, but as there might be some network gurus here:

Situation: Have an old dualie under W2K on a SpeedStream DSL modem
with a Netgear WGT 624 108g four-port/wireless router. Everything's
working nicely with FTP, web, mail, newsgroups, etc. It is the
"server" for the work group, which consists of an even older dualie
under W2K and an Inspiron laptop that connects wirelessly and which is
under a different (client) workgroup. Access and file shares are all
good.

New situation: I get a new dualie, and duplicate my other rig's
installation on it. I switch old dualie from router port 4 to 3, put
new dualie on port 4, and find my DSL immediately with full access on
Firefox, IE, newsgroups, etc.

Problem: Then I install Eudora 7, as per the old machine. Settings are
identical. On the new dualie, I can receive all e-mails and
attachments from the POP server.

But I cannot send. I have been able to send MYSELF exactly one message
(I send to an alias on the same domain...I own my own domain and it's
forwarded via my ISP to my domain name server company), and then every
attempt to send to SMTP is timed out or rejected.

And yet the old dualie, on the same workgroup, with the same settings
in Eudora, continues to send and receive perfectly. So I have a stupid
situation in which my fast new machine can't send mail, and I have to
fire up the old one on the same network to get it.

Take it as a given that my mail settings are identical.

Possible clues: On the new machine, I do not have the Netgear software
installed, as I simply identified my new box with a new computer name
on the local workgroup under W2K. Could this be that my ROUTER is
somehow interfering with access to my SMTP account? But if so, why am
I able to get one message sent to my alias, once, before all outbound
SMTP traffic goes phhftt?

Also, is there some way that a new, named machine on a designated port
could play a role in my name server redirects? I can't see how, and if
this is a local config issue, I don't want to go mucking with my mail
redirects with my domain hosting firm (I just hold the domain, I don't
run a web page or host off-site storage).

Any guesses? My work-around is "use the old machine for mail", but I
find this an annoying stop-gap. Why can I send mail from my new rig?

TIA,
R.

 

[Paul]

I rarely tread here, but as there might be some network gurus here:

Situation: Have an old dualie under W2K on a SpeedStream DSL modem
with a Netgear WGT 624 108g four-port/wireless router. Everything's
working nicely with FTP, web, mail, newsgroups, etc. It is the
"server" for the work group, which consists of an even older dualie
under W2K and an Inspiron laptop that connects wirelessly and which is
under a different (client) workgroup. Access and file shares are all
good.

New situation: I get a new dualie, and duplicate my other rig's
installation on it. I switch old dualie from router port 4 to 3, put
new dualie on port 4, and find my DSL immediately with full access on
Firefox, IE, newsgroups, etc.

Problem: Then I install Eudora 7, as per the old machine. Settings are
identical. On the new dualie, I can receive all e-mails and
attachments from the POP server.

But I cannot send. I have been able to send MYSELF exactly one message
(I send to an alias on the same domain...I own my own domain and it's
forwarded via my ISP to my domain name server company), and then every
attempt to send to SMTP is timed out or rejected.

And yet the old dualie, on the same workgroup, with the same settings
in Eudora, continues to send and receive perfectly. So I have a stupid
situation in which my fast new machine can't send mail, and I have to
fire up the old one on the same network to get it.

Take it as a given that my mail settings are identical.

Possible clues: On the new machine, I do not have the Netgear software
installed, as I simply identified my new box with a new computer name
on the local workgroup under W2K. Could this be that my ROUTER is
somehow interfering with access to my SMTP account? But if so, why am
I able to get one message sent to my alias, once, before all outbound
SMTP traffic goes phhftt?

Also, is there some way that a new, named machine on a designated port
could play a role in my name server redirects? I can't see how, and if
this is a local config issue, I don't want to go mucking with my mail
redirects with my domain hosting firm (I just hold the domain, I don't
run a web page or host off-site storage).

Any guesses? My work-around is "use the old machine for mail", but I
find this an annoying stop-gap. Why can I send mail from my new rig?

TIA,
R.

The issue is MTU. Try a smaller MTU and that email will slide
through like butter.

Try search terms like "ICMP", "fragmentation", and "black hole",
to get an explanation of the normal mechanisms used. Your SMTP
server probably has ICMP turned off, and when the MTU on your
computer is too large, the protocol fails to work properly.

Here is an article that discusses the mechanisms. Now, this
article refers to "routers" being the issue, but in my case,
only the SMTP server was the issue. Everything else I communicate
with in the world works just fine without any fiddling.

http://www.microsoft.com/technet/community/columns/cableguy/cg0704.mspx

In my case, when I phoned tech support, the answer I got was -
"No, sir, we haven't changed anything at our end recently. But
we recommend you turn down the MTU size on your computer or
on your router." Which is a pretty crappy fix, in order to talk
to that one machine.

Paul

 

[rhys]

The issue is MTU. Try a smaller MTU and that email will slide
through like butter.

Try search terms like "ICMP", "fragmentation", and "black hole",
to get an explanation of the normal mechanisms used. Your SMTP
server probably has ICMP turned off, and when the MTU on your
computer is too large, the protocol fails to work properly.

Here is an article that discusses the mechanisms. Now, this
article refers to "routers" being the issue, but in my case,
only the SMTP server was the issue. Everything else I communicate
with in the world works just fine without any fiddling.

http://www.microsoft.com/technet/community/columns/cableguy/cg0704.mspx

In my case, when I phoned tech support, the answer I got was -
"No, sir, we haven't changed anything at our end recently. But
we recommend you turn down the MTU size on your computer or
on your router." Which is a pretty crappy fix, in order to talk
to that one machine.

I recall that a very long time ago I had to fiddle with this in some
kind of win.ini file. I will try this, although it will require some
hunting with regedit open on both machines. Obviously, as I don't have
the problem on the old machine, there's a Registry MTU variable I've
set or had set for me by an installation program to enable it to work
that isn't present on the new machine's Windows 2000 Registry key in
this spot.

I'll report back. Thanks, this is a solid lead.

R.

 

[H. Seldon]

rhys bleated this on Wednesday 2/15/2006

On Wed, 15 Feb 2006 13:59:34 GMT, (e-mail address removed) (Paul) wrote:

I recall that a very long time ago I had to fiddle with this in some
kind of win.ini file. I will try this, although it will require some
hunting with regedit open on both machines. Obviously, as I don't have
the problem on the old machine, there's a Registry MTU variable I've
set or had set for me by an installation program to enable it to work
that isn't present on the new machine's Windows 2000 Registry key in
this spot.

I'll report back. Thanks, this is a solid lead.

R.

Try this url. Lots of good tests and checks including MTU
optimization.

http://www.dslreports.com/tools

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