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qmail-masq is a perl program that works along with qmail. Its purpose is to masquerade the internal mail users addresses with an external one when sending email messages from local network users to external internet users.

This add-on is useful when you configure an internal qmail mail server with either a nonexistent internet domain or a domain that you don’t own; in these cases if you send an email from the internal network, the addressee wouldn’t be able to reply (or send a new mail to that address) because this address doesn’t really exist.
This program parses every single email message passing through: if any of them has a “From:” field containing an internal user address and “To:” or “CC:” or “BCC:” to an external one, it modifies the “From:” field in order to make it seem as the sender’s email was another (it changes the email address but mantains the name of the sender).
You could also determine some “exceptions”: you can define some mail users whose address won’t be masqueraded with the default email address but with another, user-specific one.
qmail-masq could be useful even if you own the external domain and it does coincide with the internal one but you don’t want your personal address to be shown; this way any replies will arrive to an unique email.
Now with qmail-masq-0.6, even “Return-Path” will be masqueraded (to prevent rejection from other’s mail server); “Notified-to”, “Sender” and “X-Sender” fields will be erased.
The whole parameters set, such as internal domain, default email to be used in masquerading, exceptions in masquerading and debug mode can be personalized by modifying the configuration file /etc/qmail-masq.conf .
This function is already built-in into sendmail and postfix, even though just in part, but it wasn’t available in qmail, so since qmail is my favourite mail server I have written the program to make this function available there too.

You can download the latest qmail-masq version (v0.6) here
qmail-masq makes use of qmail-qfilter patch; download it from http://em.ca/~bruceg/qmail-qfilter/
To install qmail-masq read the file INSTALLinside the tar.gz pack.
You are encouraged to contribute to this program; if you have patch, suggestions or critics please contact me.

This program is Copyright(C) 2001 Davide Giunchi, and may be copied according to the GNU GENERAL PUBLIC LICENSE (GPL) Version 2 or a later version. Refeer to http://www.gnu.org/licenses/gpl.html for License details.
This software is supplied on an “as is” basis without warranty of any kind, and the author shall have no liability or obligation for damages, including but not limited to actual, indirect, consequential and incidental damages occuring out of or in connection with the use or performance of the software, without regard to whether such damages were foreseeable. Use it at your own risk.
The author can not be obliged to give any technical support or training with respect to the above mentioned software.