[Mimedefang] Re: lost input channel.

Yizhar Hurwitz yizhar at mail.com
Thu Sep 21 15:49:23 EDT 2006

> Date: Wed, 20 Sep 2006 17:19:05 +0200
> From: "J.P van Oyen" <jeepee at gids.nl>
> Subject: [Mimedefang] lost input channel.
> In my sendmail logs I see so now an than entries like:
> Sep 17 20:46:00 www sm-mta[28696]: k8IKiuOO018686: lost input channel from
> ppp-104-23.telesat.com.co [] to MTA after mail


There are several possibles reasons for that.

One of them is a layer 3 network problem - MTU related.

One host is using PPPoE or similar connection that has an MTU of 1492.

As you can see by the name,


It might be the case.

The other host (your server) has MTU of 1500.

This can cause problems because PMTU doesn't work over some routers 
firewall that block ICMP .

Here is a nice article about this:

Path MTU Discovery:

If this is the case (or might be the case), possible 
solutions/workarounds are:

* ignore if it is rare and neglect able.

* Set your host MTU to 1492 instead of the default 1500.

* Disable PMTU on your server.

* Investigate further, for example check if you can see anything common 
to the hosts that cause this.

Yizhar Hurwitz


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