While I don't have any direct experience with mimedefang, here is a suggestion:
Use the script command. Just type script filename before running a build. After you've finished the build, then you just hit ^D to logout of script. After that, you've got a full transcript of what happened during that build at filename. If you took a look through that, you may be able to check out Google for Linux for some guidance. If that fails, then you could attach the script output here.