Sendmail does not accord to the hosts order in nsswitch.conf

Dear Friend,

It is strange that my sendmail does not accord to the hosts order in
solaris nsswitch.conf. Please let me elaborate in details. Thank you.

Setting:
solaris 9 /etc/nsswitch.conf
hosts: file [notfound=continue] ldap dns

sendmail 8.13.4 /etc/mail/sendmail.cf
O ServiceSwitchFile=/etc/nsswitch.conf

hosts in /etc/hosts
host1, host2

hosts in ldap
host3



Testing result/problem
/usr/lib/sendmail can sendmail to user@host1 and user@host2, but it
cannot email to user@host3. It complains that hosts unknown.



Setting 2: Then I remove 'dns' from /etc/nsswitch.conf:
hosts: files ldap

Testing result/problem
/usr/lib/sendmail can sendmail to user@host1 and user@host2, and also
to user@host3. But sendmail cannot send email to external domain, such
as user@sun.com, because dns is removed from nsswitch.conf file.

Setting 3: I change the order of files, ldap, dns in nsswitch.conf,
but it is no luck.

I replace Solaris with Redhat ES 4, but the same problem turns up.

Do you ever meet the problem? I have been in the trouble for several
weeks. Any hints are deeply appreciated!

Best regards,
Jacky

In article
<87361457-c48d-4fda-be96-165c83cd2efd@w1g2000prk.googlegroups.com> Jacky
Wu <serenitywu@gmail.com> writes:
>
>It is strange that my sendmail does not accord to the hosts order in
>solaris nsswitch.conf.

The hosts order in nsswitch.conf governs the working of gethostbyname(),
gethostbyaddr() & Co, i.e. name <-> IP-address translation. E-mail
transport generally needs more, namely MX records, which are only
available through DNS, and per the RFCs MX records MUST take precedence
over name->IP-address mapping.

I.e. there is a mismatch between what sendmail needs and what
nsswitch.conf can provide, and sendmail tries to make the best out of
this situation: If 'dns' is *anywhere* in the 'hosts' line, MX records
are looked up *first*, and only if no MX records are found are name ->
address mappings tried in the order specified.

>hosts in /etc/hosts
>host1, host2
>
>hosts in ldap
>host3
>
>
>
>Testing result/problem
>/usr/lib/sendmail can sendmail to user@host1 and user@host2, but it
>cannot email to user@host3. It complains that hosts unknown.
>
>
>Setting 2: Then I remove 'dns' from /etc/nsswitch.conf:
>hosts: files ldap
>
>Testing result/problem
>/usr/lib/sendmail can sendmail to user@host1 and user@host2, and also
>to user@host3.

This could possibly be due to host3 having an MX record in DNS, with an
MX target that doesn't exist - but there may well be other explanations.
I'd suggest that you try to clean up your name service setup in general
instead of trying to get sendmail to hunt around in three different
services to find e-mail destinations - e.g. make sure that everything is
in DNS.

--Per Hedeland
per@hedeland.org