$H

The mail hub mc configuration

The m4 FEATURE(nullclient) (FEATURE(nullclient) on page 637) causes all mail to be sent to a central hub machine for handling. Part of what it does is to define the mc macro MAIL_HUB:

define(`MAIL_HUB', `hub')dnl

This also causes $H to be defined as hub. If MAIL_HUB has a value, and if LOCAL_RELAY ($R on page 843) does not, all local email is forwarded to hub. If LOCAL_RELAY is defined, it takes precedence over MAIL_HUB for some mail. See MAIL_HUB mc Macro on page 605 for a description of MAIL_HUB and how it interacts with LOCAL_RELAY.

You should never use this macro directly, because it might change in a future release of sendmail. Use the MAIL_HUB mc configuration macro instead.

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