Apply VDA patch to Postfix HOWTO

1. get postfix sources (you can download using wget)
2. get patch for your exact postfix version (in this case: postfix-2.2.3-vda.patch)
3. untar your postfix sources (tar -xvzf postfix.x.x.x.tgz)

# type the following at your prompt (%)
4. % zcat postfix-2.2.3-vda.patch.gz | patch -p0

result should look like this:
patching file postfix-2.2.3/README_FILES/VDA_README
patching file postfix-2.2.3/src/global/mail_params.h
patching file postfix-2.2.3/src/util/file_limit.c
patching file postfix-2.2.3/src/virtual/mailbox.c
patching file postfix-2.2.3/src/virtual/maildir.c
patching file postfix-2.2.3/src/virtual/virtual.c
patching file postfix-2.2.3/src/virtual/virtual.h