Update to 3.1.8. From the changelog:

This version fixes a bug with the recipient filters that could allow
a clever sender to use a spamdyke-protected server as an open relay.
The sequence of commands are not legal SMTP, so the sender would
have to know the server was running a vulnerable version of spamdyke
to exploit this bug.  Thanks to Mirko Buffoni for reporting this
one.

This version also fixes two problems with the idle timeout filter.
The first could cause the connection to be rejected because qmail
is slow to respond (which isn't fair).  The second was a tricky
issue where large messages from fast remote servers could be
improperly rejected because the idle timer wasn't being reset.
Thanks to Eric Shubert for reporting and helping me fix this one.

This version also fixes two compiling problems.  The first was a
problem in the "configure" script on older Gentoo installations
running gcc 3.4.6 that was treating a preprocessor warning as an
error.  Thanks to Thorsten Puzich for reporting and helping me fix
this one.  The second was a problem with CentOS 3.8, which doesn't
install the OpenSSL headers in the system include folder.  Thanks
to Bruce Schreiber for reporting this one.

(schmonz)