RE: [gentoo-user] Postfix configuration in server with dynamic IP

["Dave Nebinger" <dnebinger@joat.com>]

> My main problem is that ...
> 
> > > Currently I am using postfix for sending mail from
> > > this computer, but most of the time the IP I
> > > receive from my ISP is blacklisted and is rejected
> > > on some destinations. So I want to use my ISP
> > > mail server for sending mail (with athentication).
> 
> This blacklisted IP I receive from my ISP is
> a problem I do not know how to solve.

That's how the relayhost option in main.cf comes into play.  All email
originating from your server will be routed through the ISP's mail server
which should not be blacklisted.

So all of your email, regardless of where it is going, will pass up through
your ISP's mail server to be delivered along to the final destination.

> > There's a couple of steps that you'll need to take to get mail from your
> > system piped through your ISP:
> >
> > 1. /etc/postfix/sasl_passwd: Edit this file to include a line like:
> > 	mail.myisp.net username:password
> 
> Is it possible to use different authentications
> for diferent users on my computers? There are
> 5 users, and each user has his own email account
> in the ISP.

All you're doing with this configuration is passing email from your server
up to the ISP for delivery to the final destination; it is not going to be
altered by the ISP's mail server to change who the message originates from,
so it doesn't matter which account the email passes through.
 
> [...]
> > VERY IMPORTANT NOTE: Be sure that you're not running an open mail relay
> > (lots of info via google about how to ensure postfix is not an open mail
> > relay).  Once this setup is complete, if you were open, spammers could
> route
> > mail through your server which relays through your ISP.  From your ISP's
> > perspective you're sending the spam yourself and they could throw you
> > offline.
> 
> Is the following lines in main.cf enough to prevent that?
> 
> 	mynetworks_style = host
> 	relay_domains =

Nope, you'll want to check http://www.postfix.org/SMTPD_ACCESS_README.html
for info regarding relays.  It basically controls who can relay mail through
the server.  For example, I'm actually away from home but can relay through
my box because I've got it set up to allow my authenticated smtp relay
connection.



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