Sendmail configuration

[Craig White]

On Thu, 2008-03-20 at 08:55 -0700, Dale Farnsworth wrote:
> > If you don't have valid forward and reverse DNS for the IP you're sending 
> > from, a fair number of places will give you a 500-series error.  There are 
> > good reasons for doing that, since mail from a place that has invalid DNS is 
> > much more likely to be spam.  Get a domain name of some type; go through 
> > dyndns.org if you're small-time.  Don't neglect reverse DNS!  If "host 
> > deepan.example.org" gets you "1.2.3.4", but "host 1.2.3.4" 
> > returns "SERVFAIL", then your reverse DNS is not set.  Unset reverse DNS 
> > means you can't send mail to AOL and probably yahoo users.  NOTE:  forward 
> > and reverse DNS do not have to match, they just have to be valid names.  Lots 
> > of times, they don't match (yay for multiple domains on one box).
> 
> The requirement I've seen for AOL (and others) is that reverse DNS must
> be set, AND that forward DNS on the name returned by reverse DNS must
> point back to your IP address.  In other words, while you may have as
> many forward DNS entries as you want, there *must* be a forward DNS
> entry that matches your reverse DNS entry.
> 
> Of course, this is independent of sendmail configuration.
----
and since AOL adopted it, I have adopted the same philosophy for all
mail servers that I administrate too. It's been a good strategy.

I use postfix though, it's been easier to integrate a fairly
sophisticated strategy in deciding mail I will accept for delivery.

Craig