Put this code in a shell file called "email-if-files-changed" somewhere on your server. Then link to it from a cronjob in your crontab file using this line: 01 1 * * * root /path-to-your-custom-script/email-if-files-changed

Send email of files changed on server once per day

#!/bin/bash

FILES_CHANGED=$(find /var/www -type f -mmin -$((60*24)) -printf '%TY-%Tm-%Td %TT %p\n' | sort -r)

if [ !$FILES_CHANGED ]
then
	curl -s --user 'api:MAILGUN_API_KEY' \
	https://api.mailgun.net/v3/YOURMAILGUNDOMAIN/messages \
	-F from='Name of your server<support@yourdomain.com>' \
	-F to=support@yourdomain.com \
	-F subject='No files were changed in the last 24 hours' \
	-F text="$FILES_CHANGED"

else
	curl -s --user 'api:MAILGUN_API_KEY' \
	https://api.mailgun.net/v3/YOURMAILGUNDOMAIN/messages \
	-F from='Name of your server<support@yourdomain.com>' \
	-F to=support@yourdomain.com \
	-F subject='Files were changed in the last 24 hours' \
	-F text="$FILES_CHANGED"
fi