Building mail/mailagent hangs during running tests (basic/config). 
'filter' process starts to eat all the CPU and doesn't respond to SIGTERM.
SIGKILL works as usual.  On i386 platform there is no such behaviour.  
If I replace 'filter' binary by i386's one, the test passes.

Further investigation reveals that the following code causes SEGV on amd64, but not on i386.

--------------------------
#include <stdio.h>

int main()
{
   printf("%s\n",strerror(2));
   exit(0);
}
--------------------------

Adding "#include <string.h>" solves the problem.

logfile.c in agent/filter doesn't include string.h, and it seems to cause an infininte loop during its signal handling.

I'm not an expert of C programming, so I'm not sure whether it is a bug of
FreeBSD amd64 itself or including string.h is mandatory.

Fix: Add the following file to patch directory of the port.
How-To-Repeat: make /usr/ports/mail/mailagent as an ordinary user on FreeBSD-6 amd64.