Force nullmailer to use a fixed "from" address

As small replacement for postfix and the like, nullmailer has established on the one and other Linux home server - such as mine. My specific problem with the provider/email relay: They check if the sender email address matches the relay account email address to prevent spam. That's a good feature, but nullmailer uses actual user@host, where host defaults to the content of /etc/mailname (e.g. root@myserver.dyndns.org or www-data@myserver.dyndns.org). Nullmailer has no rewrite functionality based on config files, but in the specific case a simple (but not completely accurate) solution can be applied:

# 1) Rename the original sendmail binary:
$ mv /usr/sbin/sendmail /usr/sbin/sendmail-bin
 
# 2) Create and edit a script called sendmail:
$ touch /usr/sbin/sendmail
$ chmod 755 /usr/sbin/sendmail

Edit the sendmail script file and paste this content:

#!/bin/bash
/usr/sbin/sendmail-bin $@ -f `cat /etc/nullmailer/forced-from` </dev/stdin

The script simply forwards all arguments and the STDIN to the original sendmail, but adds the -f argument to replace the from address. In my case, I save the full sender address of the relay account in the file /etc/nullmailer/forced-from. That's it. There are two things I did not test yet:

• After done a test with PHP and "sendmail -f www-data" in the php.ini, I assume that the last "-f SENDER-EMAIL" argument that occurs will be the used one. No idea if this will be that way for all time. The argument list will have to be filtered then.

• What does the package manager/aptitude do with this when removing, updating, etc. (That's why I say not really accurate :-) )