I have a FreeBSD 4.4R machine running Sendmail (8.11.6) as a non-relaying
MTA. Sometime after last June, Sendmail decided to stop accepting mail for
local users. This happened with no changes to the local configuration.
After several hours of beating my head against a wall, I finally managed to
get it to accept mail by adding the server's names to a local-host-names
file.

At this point I'm just curious about what caused the problem. I'm no kind
of Sendmail guru, and I felt thoroughly lost in a genuine "but I didn't
change anything!" situation.

It's possible that something in our org's DNS may have changed. The machine
knows itself as mutiny.dept.example.edu (as from 'sysctl kern.hostname'),
and when we set it up that was its main DNS entry, with a DNS alias of
www.dept.example.edu. Today I saw that the DNS entries appear to have
swapped, so that mutiny is an alias for www. Would something like that
cause sendmail to reject local mail?

Thanks,
-Scott

Scott wrote:
> I have a FreeBSD 4.4R machine running Sendmail (8.11.6) as a non-relaying
> MTA. Sometime after last June, Sendmail decided to stop accepting mail for
> local users. This happened with no changes to the local configuration.
> After several hours of beating my head against a wall, I finally managed to
> get it to accept mail by adding the server's names to a local-host-names
> file.
>
> At this point I'm just curious about what caused the problem. I'm no kind
> of Sendmail guru, and I felt thoroughly lost in a genuine "but I didn't
> change anything!" situation.
>
> It's possible that something in our org's DNS may have changed. The machine
> knows itself as mutiny.dept.example.edu (as from 'sysctl kern.hostname'),
> and when we set it up that was its main DNS entry, with a DNS alias of
> www.dept.example.edu. Today I saw that the DNS entries appear to have
> swapped, so that mutiny is an alias for www. Would something like that
> cause sendmail to reject local mail?
>
> Thanks,
> -Scott

look at cf/README for DONT_PROBE_INTERFACES

Sendmail needs to have reason to believe that email addresed to a
certain domain is actually local to it instead of it being required to
relay it elsewhere, which by default it wont do.

Thats class w

So if you were relying on that feature for local mail to be accepted,
then its quite likely that whatever DNS changes were made broke exactly
that.

What you should be doing is placing the domain name explicitly into
class w, with most modern sendmail installations that means the file
local-host-names should contain names that are to be considered local
for mail delivery purposes, one per line.

In article <453813ca.164115329@localhost> nobody@xmission.com (Scott) writes:
>
>It's possible that something in our org's DNS may have changed. The machine
>knows itself as mutiny.dept.example.edu (as from 'sysctl kern.hostname'),
>and when we set it up that was its main DNS entry, with a DNS alias of
>www.dept.example.edu. Today I saw that the DNS entries appear to have
>swapped, so that mutiny is an alias for www. Would something like that
>cause sendmail to reject local mail?

That may well be the cause - sendmail takes the name of the local host
as returned by the 'hostname' command (actually the gethostname() C
function, but they should be the same), does a DNS lookup on it - and
IIRC enters *only* the returned "canonical name" (plus some abbreviated
forms of that) in class {w}, the list of names that are considered
"local". I.e. if the name of the host is actually an alias (CNAME record
in DNS), it won't be in class {w} I believe - and having such a setup
may well cause other problems too.

--Per Hedeland
per@hedeland.org