I have for the past few weeks trying to get my machine to not do a DNS lookup
when I send a mail to the queue. I have lurked on this mail list and the
linux-diald and found that the suggestion to remove the ability to lookup is
to add FEATURE(nocanonify) to your .mc file.
I eventually bought the Bat book, not because the advice I read was incomplete
but because I needed more information, and was surprised to find in �16.5 that
adding nocanonify is potentially a problem.
In short, if there is an unqualified (non canonical name) in a cc: or bcc:
field and the mail goes to an alternate mail hub referred to by an MX record,
the second, copied to, address may not get resolved. Quoting the Bat book
�Before allowing unqualified addresses to go out from a client, be sure that
there are no offsite MX records and that there are no plans for any.�
I have got sendmail to stop carrying out a DNS lookup by creating a restricted
service switch file which contains the following:
----/etc/send_switch.conf----
passwd files
hosts files
aliases files
----end file----
and including the following in my .mc file:
define(`confSERVICE_SWITCH_FILE', `/etc/send_switch.conf')
As an aside you should be aware that this does not work if the services have a
colon at the end e.g. �hosts:� as opposed to �hosts�. I thought the former was
the correct syntax for a service switch file.
I can see why a standalone machine does not need to canonify addresses because
all mail will leave the site and therefore is usually fully qualified.
But if removing DNS lookup is relatively easy, why get into bad habits?
------------------------------------------------------------
Richard McMahon
Copenhagen
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