Accepting certain unresolvable domains

Occasionally, you may want to selectively permit mail from unresolvable domains. As an anti-spam measure, most mail transport agents, including Sendmail, do not accept email from unresolvable domains by default.

To globally accept email from unresolvable domains in Sendmail, you may use the ACCEPT_UNRESOLVABLE_DOMAINS feature. However, it is often better to selectively permit unresolvable domains in Sendmail using the access database:

1. vi /etc/mail/access

2. Add the following entry:
unresolvable_domain ok

Note that this will allow mail from unresolvable_domain and all subdomains (e.g. host.unresolvable_domain).

3. Build the new Sendmail access database.
makemap hash /etc/mail/access < /etc/mail/access

The change takes effect immediately after rebuilding the access database.

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Last modified: 04/30/2003