Sendmail on a LAN

Bill Davidsen davidsen at
Wed Aug 18 14:07:46 UTC 2010

JD wrote:

> I have done all that. Really. ISP (at&t) has unblocked port 25
> per my request. So I can indeed smtp out. But when an smtp request
> comes in to the router, the router seems to get confused as to the
> session type - and calls is an Unknown session type, and blocks
> the request. Router has no settings as to what session types are
> and what types can be blocked, and what types can be accepted.
> Session types are opaque to the user as far as configuration goes.
> There are no means to admin session types.
> What else can one expect from a thuggish isp?
You have run tcpdump on port 25 inbound to verify that the router is the 
problem, right? Suggest saving all packets to a file for a few hours, then using 
either tcpdump or wireshark to look at them, or not look at them if your router 
is doing what you think it is.

And be sure that the unwanted packets are inbound and not the result of your 
sendmail sending back something unexpected.

Bill Davidsen <davidsen at>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot

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