October 2007
Intermediate to advanced
1308 pages
161h 13m
English
Content preview from sendmail, 4th EditionBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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FEATURE(accept_unresolvable_domains)
Beginning with V8.9, sendmail
will refuse a mail message if the address specified
as part of the SMTP MAIL
From: has a domain part that cannot be
looked up. For example, if the domain
foo.bar does not exist, the
following error will be logged with
syslog and the message will
be rejected with the same error message:
553 5.1.8<user@your.domain>... Domain of sender address other@foo.bar does not exist
If the domain cannot be looked up, the result is a temporary error:
451 4.1.8<user@your.domain>... Domain of sender address other@foo.bar does not resolve
We recommend rejecting such addresses, but there might be circumstances in which you cannot. If, for example, you are behind a firewall and lack access to full DNS lookups, you might want to accept everything. But if that is the case, you will need a sending mail hub with good DNS access so that you can reply to such messages.
You can accept such addresses by defining the FEATURE(accept_unresolvable_domains):
FEATURE(`accept_unresolvable_domains')
This tells sendmail to accept all
envelope-sender addresses, even if the domain part
following the @
cannot be looked up with DNS.
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.