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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