Sendmail on a LAN

Daniel B. Thurman dant at
Tue Aug 17 22:35:57 UTC 2010

 On 08/17/2010 02:25 PM, JD wrote:
>   On 08/17/2010 01:27 PM, Gordon Messmer wrote:
>> On 08/17/2010 09:33 AM, JD wrote:
>>> Re:  a.b.c.d ==>
>>> and ==>   a.b.c.d
>>> does not seem to apply to the google smtp server I use for Thunderbird.
>> You did your test entirely backward.  You did a forward lookup first,
>> and then checked the PTR of the IP which was returned.  There is no
>> requirement for a PTR to match every hostname that resolves to its IP
>> address.
>> Let's finish your test:
>> $ host
>> is an alias for
>> has address
>> The result of this test merely identifies an IP address.  Now, let's
>> test to validate that the IP returns a PTR that resolves to the same IP:
>> $ host
>> domain name pointer
>> $ host
>> has address
>> Yep, totally valid.  That IP address has a PTR record, and the hostname
>> contained in that PTR resolves back to the same IP address.  This host
>> is properly configured.
>>> So, Thunderbird client does not seem to mind that
>>> reverse lookup does not match the name
>> Clients rarely do.  It's the servers to which you're going to try to
>> deliver mail that will mind.
> I see! Thanks for the heads up!
> At any rate, I am having serious problem with an unwieldy router.
> I just posted a message about that.
1) Make sure your ISP is not interfering with your traffic, to direct
    all traffic to/from your primary router static IP address.  You can
    call them and ask about it.  Mine was very helpful and cooperative
    ( and their rates are good compared with many I have

2) If your ISP router allows, you might be able to set up your router
    as a pass-through router forwarded to a more robust FW router,
    or directly to your fedora box to handle the public firewall/NAT.
    I have a hardware firewall appliance (SonicWall), so my dumb ISP
    provided router is simply a pass-through router to SonicWall.

3) You state that you have static public IP addresse(s), but do
    you have a domain name?  If so, make sure at the domain
    name provider (DNP) website that you define your name
    server addresses and most DNP require at minimum, 2
    name servers. I set my name servers to ns1.mydomain.x1
    and ns2.mydomain.x2 which is handled by my own domain
    name servers. Just make sure you configure your name servers
    properly (forwarders to your ISP name servers).

    Make sure your sendmail is also properly configured.  Since
    you use Thunderbird as I do, it is IMAP capable, so sendmail
    needs special setup to support IMAP/Mailldir (as opposed to mbox)
    handling and I use dovecot as my IMAP server As for the many
    spams that DO come through, I use sendmail for that - I get VERY
    MINIMAL spams - and this requires that you carefully and properly
    setup your sendmail configuration.

Once you get though all of this and to make it work, it is well worth it,
at least it is for me.


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