A simple script that re-indexes emails using mu and sends a notification if new emails are detected.

mu-index-notify.sh

# puts timestamps into an easily comparable format
extract_timestamp() {
   local RAW="$(echo "$1" | cut -c1-31)"
   echo "$(date --date="$RAW" '+%Y-%m-%d:%H:%M:%S')"
}

# removes html characters that are interpreted poorly by dunst
format_string() {
   echo "$1" | sed 's/>/\&gt;/' | sed 's/</\&lt;/' | sed 's/\$/\\$/'
}

# locate the timestamp of the newest message
NEWEST_PREFETCH_MSG="$(mu find -z 'date:today' | head -n 1)"
NEWEST_PREFETCH_MSG_TIMESTAMP="$(extract_timestamp "$NEWEST_PREFETCH_MSG")"

# reindex all emails using mu
mu index --maildir ~/.mail

# grab the newest ten emails that are created today and unread
RECENT_TEN="$(mu find -z 'date:today' 'flag:unread' | head -n 10)"

# maintain the last timestamp to prevent duplicates
LAST_TIMESTAMP=""

# iterate over each message
while read -r msg; do
  MSG_TIMESTAMP="$(extract_timestamp "$msg")"
  # check if message is newer than previously newest message and not duplicate
  if [ "$MSG_TIMESTAMP" \> "$NEWEST_PREFETCH_MSG_TIMESTAMP" ] &&
     [ "$MSG_TIMESTAMP" != "$LAST_TIMESTAMP" ]; then
    # emit a desktop notification with the email sender and subject
    MSG_SENDER="$(echo "$msg" | sed -r 's/^.{32}//' | sed 's/>.*$/>/')"
    MSG_SUBJECT="$(echo "$msg" | sed 's/^.*> //')"
    # Emit proper notification when run as super user
    #sudo -u gilbertw1 DISPLAY=:0 DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus notify-send "$(format_string "$MSG_SENDER")" "$(format_string "$MSG_SUBJECT")"
    notify-send "$(format_string "$MSG_SENDER")" "$(format_string "$MSG_SUBJECT")"
  fi;
  LAST_TIMESTAMP="$MSG_TIMESTAMP"
done <<< "$RECENT_TEN"