MaxBroome

If you only need a receiving and catch-all address. You could use Cloudflare’s relay service. It’s totally free with the exception that you can’t send email but only have them forwarded to another email address, such as your personal email address.

It’s super easy and quick to setup, and if your domains aren’t already behind Cloudflare you should do it, it really is great.

If Ubiquiti isn’t your jam, might I suggest pfSense. Most of the features of Cisco but easier management with the web UI and no license.

This. Cloudflare also has this relay option that I use for my domain. We have got to start telling people to stop hosting their own mail server and just use a relay. It’s far too much of a headache.