Domain of sender address ... does not resolve

[Phil Meyer]

Bill Davidsen wrote:
> I just did a new FC9 (fully updated) install, and it regularly rejects 
> outgoing mail with the subject error message. The address does 
> resolve, of course, so I'm not sure what it means instead of what it 
> says.
>
> The nameservers in /etc/resolv.conf are the authoritative DNS for the 
> domain, both are up, etc.
>
> Someone have a clue?
>

Do reverse lookups work?

Often, forward lookups work and reverse do not, ie:

host domain.name
vs
host NNN.NNN.NNN.NNN

Sendmail is trying to do a reverse lookup.

It will tell you in the error message which host name or IP does not 
resolve.  Check it both ways.

Good luck!