[Q] renattach doesn't work! Mail bounces.
[A] System logs (and www.google.com/linux) are your friends! ;)

> "|/usr/sbin/renattach -b"
>     (reason: 550 Unsafe for mailing to programs)
>     (expanded from: username)

For some reason sendmail has decided that it doesn't want to allow
this. There are a few possible reasons:

- Permissions on .forward might be too loose. Try
chmod 640 .forward

- sendmail restricted shell (smrsh). This is mentioned in the
renattach manpage

Edit sendmail.cf and look for the line that refers to the restricted shell.
Try searching for "restricted shell" and "smrsh". The renattach executable
has to be placed in this directory, it might be /usr/libexec/smrsh or 
/etc/smrsh from what I've seen so far.