I am still actively using a 32-bit intel laptop.  It's running my stopgap server.  The one this thread was originally about.  It's an ASUS netbook from 2008 -- the first one that required no proprietary drivers.

I wonder sometimes if I have the machine correctly configured, but intead might it be too slow to respond to the DNS requests for it to be regarded as authoritative.  Is this remotely plausible?

It takes me about 20 seconds of wait time to connect to it using
    ssh topoi.pooq.com
That's 20 real-time seconds to get to the shell prompt.  Ten seconds before get to enter a password, and after that another ten seconds to get to the shell prompt.

-- hendrik

It wouldn't have to send a message back to the sender.  The sender's email address is on one of the headers in the message itself.  But it might want to check if the sender actually exists or is just a randomly generated email address.

I have no trouble using dig to get the DNS information including the MX.  And it's using the 1.1.1.1 DNS server when it doe this (as configured in resolv.conf.

My olld server had a nontrivial email configuration.
I suspect I have to look into the SMTP configuration of the laptop I pressed into service as my stopgap server.  I suspect I was lulled into complacency by email apparently just working.  It now seems it was just apparently, not really.  Upon checking, I have trouble sending to gmail as well, and quite possible sending to everywhere.

I'll be looking at my backups from the old server for details.

Sorry to have bothered everybody.  But I'll continue doing it if I run into new problems and I will provide a success message when I finally do succeed.

-- hendrik

Indeed.  I think it is quite likely that the problem is in my network setup, and I thank you for confirmation.
I'm hoping someone will suggest things to investigate to help track down the problem.

-- hendrik