# remove all headers added in the *local* mail chain:
#   1. added by this mailfilter
#   2. added by the retraining system
#   3. added by offlineimap
#   4. added by the MUA
:0 fw
|$FORMAIL \
          -IX-EqDomain -IX-EqTo -IX-Justme -IX-Spamtrapped \
          -IX-Delayed -IX-Tickle -IX-Resubmitted \
          -IX-Trained-As \
          -IX-UID -IX-OfflineIMAP- \
          -IX-Status -IStatus -IX-Keywords -IContent-Length

# now should be idempotent