Ever since Google dropped the free version of Google Apps for Business (now known as GSuite), I've been on the hunt for a simple, easy to set up service that won't charge me for a simple mail server. For about a year, I've been using Pawnmail for my silly, prospective, and low-traffic domains.
The service is run by donations, and I love how the maintainer is upfront about how many days of runway are left. It's unclear what happens when you hit the 2GB limit -- but in my case if I'm using that much mail, I'll move to something with some semblance of a reliability promise.
For the many domains I have bought for small projects or laughs, it's great to be able to set up emails without the ceremony of the other free email servers I've found.
While I wouldn't rely on Pawnmail for business-critical emails, it does a fantastic job of being a bare-minimum, totally transparent service.
In a time where every "feature" startup seems to be trying to pivot to SaaS or Freemium, it's refreshing to see a service that is content doing one thing well and providing a truly free (as in beer) service.