As it turns out, running an email server from a home broadband connection is unnecessarily complicated. In the past, I didn't need a local server; Gmail was willing to handle all the traffic as long as it was from a known gmail.com address. I used email@example.com
Life was simple. Then Google decided simplicity was a bad thing, and my simple link from the Holographyforum software to Gmail stopped working.
Only until just recently did I finally have the time and ambition to install and configure a local email server. Sending email was surprisingly easy, or at least so I thought. Receiving mail was fraught with twists and turns (all of which I had created for myself as it turns out, but that's a different story). Finally, oh blessed finally, I had it all working...only to find out that my Internet provider reports all their residential IP address blocks to SpamHaus, and there are some email servers out there that do not accept email from servers listed by SpamHaus. (Ironically, my own Internet provider is one that rejects my email.)
As it turns out, and much to my surprise, there are a couple of (free!!) services that will relay email from my email server, completely bypassing the SpamHaus blacklist.
So, with the email server reconfigured to forward outgoing email to the relay, I am now mostly confident email is again working properly.