Re: How getmail deals with delivery errors and with bounce e-mails

On Tue, 2020-11-03 at 22:02 +0000, mick crane wrote:
> On 2020-11-03 21:17, Langenxx Feld wrote:
> 
> > I also do not understand why I should use other.domain.org
> > internally.
> > I purchased domain example.org , so I will be using it internally
> > too.
> > Why do you want to introduce other.domain.org in the equation?
> 
> I don't think it is a good idea to have the domain resolving to your 
> hosting service and also internally to your mail server.
> As I'm understanding things the local network wants to be .home or 
> something.
> 
I agree with Mick. Its not a good idea: I've seen it cause confusion:
see below.

I use my principal domain name both as the destination for incoming e-
mail arriving at my LAN and as the domain name for one of my websites: I
have two, both hosted externally and using entirely different domain
names but one of the websites has the same domain name as the gateway to
my LAN, i.e the website is www.example.org hosted by Zen. Incoming mail
is addressed to [email protected] and passed on by by Zen's smarthost.
This has worked well for some years without any problems showing up.

So far, so good, but I recently added a data input page to the website.
This accepts a set of parameters from a visitor and then calls a small
PHP program that creates an email containing the parameters and sends it
to [email protected] - i.e. a user name on a host on my LAN.

My hosted website defaulted the sender address to [email protected] which
in turn confused Postfix into rejecting the message due to an 'internal
loop' because the sending and receiving domain names are the same. After
a lot of headscratching and experimenting I got it sorted out by forcing
PHP to set the From, Return-Path and Reply-To headers to falsely say
that the message is from my other hosted website, [email protected] w
hich is on the same Zen web server.

That took a lot of time to fix, not least because I couldn't find
anything on the web that was even remotely similar to this problem.

So, short answer: do NOT duplicate a host name in any situation where
the originating and destination MTAs have the same domain name and might
exchange messages. 

Martin