Sendmail on a LAN

Gregory Woodbury redwolfe at
Mon Aug 16 19:24:58 UTC 2010

On Mon, Aug 16, 2010 at 1:46 PM, JD <jd1008 at> wrote:

>  I read the wiki for setting up and configuring sendmail
> Clearly, a full setup of DNS server for your domain
> must be set up, per this wiki, along with mx records ...etc.
> Does this prevent one from settiing up and using sendmail
> on a LAN to send and receive email to/from the outside world?

In a word, no.

Get a name for your router public ip address and set up at
dyndns to get mail delivered to that name.  Set your router to forward
incoming SMTP
to the appropriate machine and go from there.

> The main router is set up to forward all necessary ports
> (smtp, pop, pop3, ....etc) to the machine which would run
> sendmail. The firewall on the machine is set up to allow
> packets to/from these ports.
> I understand that some things need to  be set up so that sendmail
> sends headers that use a routable IP address as the source of
> the message. Is it possible to make sendmail use my router's
> public IP address in the message headers? How?

Sendmail doesn't use IPs *per se* but using the name you get is necessary.
For example (some names changed to protect the guilty):

my machine "masquerades" as with the MX for that domain
pointing to my router's name via The router port forwards 25 to
appropriate machine and the conversations carry on as usual.

Outgoing, I have sendmail using gmail as my smart host, with appropriate
authconfig settings for my gmail account.

The key is to "MASQUERADE AS" in the file.
This tells sendmail to use the name you want.

Hope this Helps
G.Wolfe Woodbury
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