Mailinglist Archive: opensuse (3337 mails)

< Previous Next >
Re: [SLE] mail sending and Postfix was OT: Posting from another unsubscribed address for a subscriber?
  • From: "Hylton Conacher (ZR1HPC)" <hylton@xxxxxxxxxxxx>
  • Date: Thu, 20 Apr 2006 13:08:13 +0200
  • Message-id: <44476B9D.3030604@xxxxxxxxxxxx>
THANKS Carlos, my reply/understanding is in-line.

Carlos E. R. wrote:

The Sunday 2006-04-16 at 18:59 +0200, Hylton Conacher (ZR1HPC) wrote:


By the way, tiscali.es is out of business. They sold their customers
et al to "Wanadoo" (France Telecom España S.A).

Tiscali went out here about 6 montha ago and now the servers are owned
by the MWEb ISP. They are, at teh moment, keeping the server names that
Tiscali used but I am sure they will change to xxxx.mweb.co.za in a while.


¡Ha! So, it wasn't only Spain where they failed. Interesting.
Obviously they, in what ever country, did not care about their customers.

Sorry I need a bit of explanation here.

Do I understand correctly that once you have dialed in and authenticated
that the Postfix server just uses the internet connection and actually
not the ISP's SMTP server, other than as a SMTP relay?

Ok, let's see. There are different methods.

Many accounts provide a pop/imap box, plus an smtp server. With programs like mozilla you can configure each account separately, each with their different fetching and sending methods.

On the other hand, good isps may, or should, provide and smtp server which you may use to send all your email, regardless to which account they belong. Consider: you may have your own domain name, but you do not have your own sending server, so you use the smtp server of the isp for that purpose.
Well I have a domain with another ISP and dial into Tiscali, just as the access is paid until Nov 2006 already, and I've been with the same ISP thru 3 takeovers and since 1990.

What can your postfix do?

By default, postfix (or sendmail, or whatever) will send mail on its own, without the help of any other smtp server. Postfix is an smtp server, so it can send email to any destination by its own resources.
OK, understood that Postfix is the MTA.

What happens it you are on dial-up? Mainly, you do not have a fixed IP. Coupled to that, reverse dns will not work, or will not point to your name. Can you still send mail directly? Sure! well... not quite. Many recipient servers will frown on it and refuse receiving email from you, because many spammers have abused and used the direct send method to bypass controls. Fortunately, SuSE has not implemented that policy, not absolutely, at least.
It would seem that even setting up my own Postfix server at home would not help with all the SMTP mail authentication to prevent spammers.

Your postfix can be told to use a relay server based on the destination (the "transport" table), for those cases that the recipient server refuse talking to you. Unfortunately, for us, it is not possible, or I don't know how, to select diferent relays based on the from addres, as we can do with Mozilla.
Such is life on dial-up :P

So in essence, provided an individual/company uses the ISP of their domain holder(ISP-1), they can use the ISP SMTP servers. If an individual/company wants to obtain a domain at another ISP(ISP-2) and dial into ISP-1 to send mail from the IAP2 domain, it is not 'allowed' to cut down on spam?

There is something I am missing however :(
Something about the authentication :(

What hapens to folk who maintain their own SMTP servers(Postfix/Sendmail etc)? Are they still restricted in sending mail from another another domain(ISP-2) via a different ISP(ISP-1)?

Let me illustrate with an example on how I understand the SMTP process:

1. Assume that I had a two domains registered, each with a different
ISP.
ISP-1 www.global.co.za
ISP-2 www.conacher.co.za

2. I have a single Postfix SMTP server for both domains, but I cannot
afford to keep it online 24/7 and so I have a dialup account with
ISP-1.

3. On first dialup to ISP-1 my SMTP server authenticates and retrieves
its dynamic IP from ISP-1. It first sends the outgoing email from
both domains to the next closest SMTP server(ISP-1's SMTP server) and
then receives email from POP mail stores at each domain. My SMTP
server then disconects itself from ISP-1.

4. The mail received by ISP-1's SMTP server is marked as certified as
ISP-1 was able to confirm that the sender was someone who they knew
and who had dialed into the ISP-1 network. The message details from
the message sender do not matter as they came from an authenticated
source. If there is a problem with one of the messages sent then
ISP-1 will be able to identify me as the sender and I could face
legal action.

5. The mail leaves ISP-1 and is received by the next SMTP server. That
SMTP server does not need to authentiacte the messages it has
received from ISP-1 as they would only have been forwarded onto the
net if they had been authenticated by the originating ISP.

6. The third SMTP server delivers the mail into the mail store of the
recipient, sending back any return receipts requested.


What am I missing in steps 3/4/5. Does each SMTP server need to authenticate the sender, why?

Are dialup postfix SMTP servers an option or are they really just POP message stores?

I am going to need to set-up a Postfix server closely resembling the above example and I wonder if it is possible and or if thre are caveats?

Tnx again Carlos et al.


< Previous Next >
Follow Ups