Preventing Connection Timeout in SMTP session

I have a Mail Transfer Agent (MTA) running on Windows 2000.
The problem is SMTP sessions time out with major mail
services like yahoo.com and hotmail.com.

Trying telnet yahoo.com 25 at a shell prompt, I see the
connections timing out in less than a minute.

The MTA (exim, built with cygwin) allows you to set
SMTP timeouts. The default is 5 minutes.

The documentation says this setting is bounded by the
system setting for (SMTP) timeouts, however.

So, I want to know how I can adjust TTL, for SMTP
sessions, and for all TCP/IP sessions in general
on Windows 2000.

 

You should be able to set TTL on your DNS MX records. Would that solve the problem?

 

I googled for some info on TTL in MX records and it
appears it's only for name servers which want to use
the information and cache it. The TTL indicates how
long this information is valid.

From https://gns.nominum.com/doc/english//glossary.html

Each [30]Resource Record in the DNS has a TTL (for time-to-live)
field. This fields instruct remote, [31]caching nameservers to forget
the records after the specified time, so that said nameserver will
have to fetch a new copy from an [32]authoritative nameserver the next
time the record is desired. It may then cache that new resource record
for the time of its TTL field.

I think TTL was not the right term. I don't really
know even if it is a Windows 2000 configuration problem,
because at times I see Destination host unreachable
messages from the sub network the machine is on at
the same time as I can connect from the school's main
mail server. The unreachable hosts are not at school, however.

 

Greg - sorry but this mail thing isn't an area of expertise for me at all.

And you probably didn't want TTL. It is badly mis-named because it is really a hop-count value. A TTL of 128 (the default with ping) means the packet will have the TTL value reduced by 1 every time is is passed along by a server and if it reaches 0 before it reaches it's destination, the packet is discarded.

I agree that you do are looking for some sort of timeout value and I have no idea where/how you would set one.

But stay with the thread. We do have a couple of mail folk posting on here and with this thread bounced to the top and having some activity, it is likely to be picked up by someone who can help.

 

The problem may (or may not) have to do with telnetting

Just because you are telnetting on port 25 (SMTP default port) doesnt mean that you are using an SMTP packet - its still a Telnet port 21 packet

Any decent firewall (and we assume that people like Yahoo would have one) will strip the packet down and examine it, a 21 packet masquerading as a 25 packet will be treated as very suspiscious and dropped

Depending on the way they do firewalling its possible (though not very likely) that this will actually add you to some sort of blacklist as you appear to be a hacker

Doesnt solve your problem but may be food for thought

 

> Just because you are telnetting on port 25 (SMTP default port) > doesnt mean that you are using an SMTP packet - its still a
> Telnet port 21 packet

I didn't know that. I think ordinary telnet is 23 and FTP is 21.

Just to check that yahoo is not screening on whether it's coming
in a SMTP packet or not I tried using SMTP protocol from a
command line prompt and I was able to get a very short email
through. Other attempts failed because I took too long to write
some headers, I think, and the connection closed on me.

So at least, they haven't tightened the gates that much yet.

As for my Connection time out issue, the guys at the computer
center here have recognized a routing issue from the subnet
I am on, and it seems to have gotten even worse with a new
router they have apparently installed to combat a Red Code
wave.

Perhaps because no one here told me how to adjust Connection time out periods for Windows 2000, connections don't time out.

On the other hand I noted from a 1998 message archived here that you could adjust Internet Explorer connection timeouts through the registry, so perhaps there is some setting in Windows 2000.

Anyway, thanks for the support.

Depending on what the computer center does about my problem, I will be back to report.

 

Here is a quickie article on adjusting SMTP timeout periods on a client PC which is the only thing I'm familiar with doing. OE has the same feature as probably do the other major mail programs.

and Here for one sort of ftp client.

But I thought you were speaking of some way to adjust the mail server itself.

 

My apologies 21 is indeed FTP - teach me to type in a hurry !

Rest of the post still stands for the principle involved