PostSRSd provides the Sender Rewriting Scheme (SRS) via TCP-based lookup tables for Postfix.
/etc/default/postsrsd
mkdir -p /etc/postsrsd
[ -e /etc/postsrsd/postsrsd.secret ] || { dd if=/dev/urandom bs=18 count=1 2>/dev/null | base64 > /etc/postsrsd/postsrsd.secret; chmod 600 /etc/postsrsd/postsrsd.secret; }