なんだかウェブに出てる情報が怪しく…。RHEL 7.4のspamassassin-3.4.0-2.el7.x86_64とprocmail-3.22-36.el7_4.1.x86_64で動作確認
SHELL=/bin/bash
PATH=$HOME/bin:/usr/bin:/usr/local/bin
MAILDIR=$HOME/Maildir/
DEFAULT=$MAILDIR
LOGFILE=$MAILDIR/procmail.log
:0fw: spamassassin.lock
#*!^X-Spam.*
| /usr/bin/spamc
:0
* ^X-Spam-Status: Yes
.Junk/
