Re: Sendmail on a LAN

On 08/17/2010 08:47 AM, Gordon Messmer wrote:
On 08/16/2010 10:46 AM, JD wrote:
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?
Not by itself, but I don't like the advice in that tutorial. It
suggests a configuration with a catch-all address. Long-term, you'll
find that you have to turn this off or else your catch-all will receive
an enormous amount of spam sent by spammers who used a dictionary attack
and found that every address they test is valid on your system. Without
a catch-all, there's no purpose in using the virtual user feature at
all, so the howto is somewhat more complicated than it needs to be.

Beyond that, it does not address several practical concerns with setting
up a mail server. First, you'll need a static address and a proper PTR
for it. You won't be able to set up a PTR without a static address, and
if the reverse lookup for your IP address isn't valid, many systems will
refuse your mail. The reverse lookup (PTR) for your address must be a
hostname that resolves to your IP.

aa.bb.cc.dd -> PTR myhost.example.com
myhost.example.com -> A aa.bb.cc.dd

You should also look up your IP address on a blacklist watcher:
http://www.dnswatch.info/dns/rbl-lookup

If you're listed in one of the dynamic IP blacklists, you want to set up
a smart host through which you'll relay mail. Many sites will otherwise
reject your messages. Likewise, if your ISP prevents you from making
outbound connections to port 25, you'll need to use a smart host,
because you couldn't send mail any other way.

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?
No, that's not quite right. Sendmail should be configured to use a
valid hostname for HELO, but the IP address will be recorded in a header
which is set by the receiver of the message. You can't do anything to
change that.

Well, that's very interesting.
I am on the verge of giving up.

Re: a.b.c.d ==> valid.host.name
and valid.host.name ==> a.b.c.d

does not seem to apply to the google smtp server I use for Thunderbird.
To wit:

$ nslookup
smtp.gmail.com
Server: 156.154.70.1
Address: 156.154.70.1#53

Non-authoritative answer:
smtp.gmail.com canonical name = gmail-smtp-msa.l.google.com.
Name: gmail-smtp-msa.l.google.com
Address: 74.125.127.109


74.125.127.109
Server: 156.154.70.1
Address: 156.154.70.1#53

Non-authoritative answer:
109.127.125.74.in-addr.arpa name = pz-in-f109.1e100.net.

Authoritative answers can be found from:


pz-in-f109.1e100.net
Server: 156.154.70.1
Address: 156.154.70.1#53

Non-authoritative answer:
Name: pz-in-f109.1e100.net
Address: 74.125.127.109


So, Thunderbird client does not seem to mind that
reverse lookup does not match the name smtp.gmail.com

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