If a MASQUERADE_AS domain is defined, that name replaces any sender addresses, the domain part of which is listed either by MASQUERADE_DOMAIN (Section 4.4.3), or in the $=w class ($=w). The allmasquerade feature causes header recipient addresses to also have that treatment.

But note that this feature can be extremely risky and that it should be used only if the MASQUERADE_AS host has an aliases file that is a superset of all aliases files and a passwd file that is a superset of all passwd files at your site. To illustrate the risk, consider a situation in which the masquerade host is named hub.domain and mail is being sent from the local workstation. If a local alias exists on the local workstation—say, thishost-users—that does not also exist on the masquerade host, this allmasquerade feature will cause the To: header to go out as:

To: thishost-users@hub.domain

Here, the address thishost-users does not exist on the masquerade host (or worse, possibly as an address somewhere out on the Internet), and as a consequence, replies to messages containing this header will bounce.

The form for the allmasquerade feature is:

MASQUERADE_AS(`your.hub.domain')
FEATURE(`allmasquerade')

Note that MASQUERADE_AS (Section 4.4.2) must also be defined and must contain a fully qualified hostname.