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:
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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