HP-UX Mailing Services Administrator's Guide

Configuring and Administering Sendmail
IPv6 Support
Chapter 2 73
IPv6 Support
An option value inet6 is provided for the field Family in
DaemonPortOptions to enable IPv6 functionality.
To enable IPv6, set the DaemonPortOptions in the sendmail.cf
configuration file as follows:
O DaemonPortOptions=Port=smtp, Name=MTA, Family=inet6
This will enable Sendmail to accept both IPv4 and IPv6 addresses.