How do I get mailutils working properly?

Using this guide here I installed tripwire: https://www.digitalocean.com/community/articles/how-to-use-tripwire-to-detect-server-intrusions-on-an-ubuntu-vps

During this guide there’s a section where you install mailutils and you’re suppose to send an email to test both that tripwire and mailutils is working. However even after configuring my iptables to allow port 25 for SMTP I receive no emails at my email from the VPS.

I’ve setup iptables, and fail2ban using digitalocean tutorials. My iptables look like this:

-P INPUT ACCEPT -P FORWARD ACCEPT -P OUTPUT ACCEPT -N fail2ban-ssh -A INPUT -p tcp -m multiport --dports 8080 -j fail2ban-ssh -A INPUT -i lo -j ACCEPT -A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT -A INPUT -p tcp -m tcp --dport 8080 -j ACCEPT -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT -A INPUT -p tcp -m tcp --dport 25 -j ACCEPT -A INPUT -j DROP -A fail2ban-ssh -j RETURN