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I'm setting up a postfix mailserver and I've run acrossed "Address masquerading".

The description from the documentation says

Address masquerading is a method to hide hosts inside a domain behind their mail gateway, and to make it appear as if the mail comes from the gateway itself, instead of from individual machines.

What does this actually mean and what does the mail server do with masquerading?

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up vote 8 down vote accepted

SMTP address masquerading is the replacement of the host portion of the "From" address on an email with another address. Imagine you have, say, the following SMTP servers in your organization:


By default, most SMTP servers would show mail sourcing from these machines as being from "", "", etc.

You'd like emails sourced by the SMTP servers on each of those machines to appear "From" the "" domain. You could configure address masquerading on each of those server computers to make them source mail as "". Postfix also supports doing this on a single "gateway" SMTP server (i.e. a server that all the other machines relay SMTP thru) such that it does the rewriting in a central place.

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It's called masquerading because you have a server, say, that is talking to the world as if it is, for example. Or the reverse, a mail server on that accepts EMail for several domains and, for example, in each case saying it is the server that the EMail is arriving for.

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