Open Source Email

ISPConfig

Zimbra

Mailcow

Cuttlefish (not a mail server, but an open source alternative to transactional mail services like Mailgun and Sendgrid).

Postal is another product like Cuttlefish

hMailServer

iRedMail

Omeka

Omeka is an Open-source web publishing platforms for sharing digital collections and creating media-rich online exhibits

Open source anti-spam solutions

There are more out there than I thought.  All of these are free and current as of this post.

ASSP, Anti-Spam SMTP Proxy Server

EFA Project, Email Firewall Appliance Project 

Mailscanner, with a web front end called MailWatch

RSpamD

Scrollout F1

Spamassassin, from the Apache Foundation

 

Web interface for the dig command

Web interface for the dig command.  

https://www.digwebinterface.com