Sendmail configuration

[Dale Farnsworth]

> 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.

-Dale