Sendmail on a LAN

Daniel B. Thurman dant at
Wed Aug 18 02:50:08 UTC 2010

 On 08/17/2010 05:10 PM, JD wrote:
>   On 08/17/2010 04:56 PM, Craig White wrote:
>> On Tue, 2010-08-17 at 16:47 -0700, JD wrote:
>>> On 08/17/2010 03:35 PM, Daniel B. Thurman wrote:
>>>>    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
>>>>       checked.
>>>> 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.
>>>> FWIW,
>>>> Dan
>>> 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?
>> ----
>> configure your router to forward inward port 25 (TCP) to your mail
>> server. Shouldn't be that hard to do.
>> Craig
> I have done more than that.
> For all incoming requests (ports 1-65535) are forwarded to my fedora 
> machine,
> for both tcp and udp.
> Problem seems to be the firmware of the router (made by 2wire for at&t).
> it is absulutely the most horible router firmware I have ever used.
> here's an example of it's brain dead operation:
> src= dst= ipprot=6 sport=49645 dport=25 Unknown 
> inbound session stopped
> And yet, it is confugured to ACCEPT smtp packets.
> It makes the lame excuse it does not know the inbound session?
> What a bunch of unmentionable stuff!!
What is this router you are talking about?  Are
you sure it isn't broken or is in need of a firmware
update?  I have no clue what this router is that you
are dealing with...  care to provide a bit of details
since you are bitterly complaining about it?

If all else, consider getting another router that you
know how to configure?

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