[kwlug-disc] msmtp email to gmail not landing - ideas?

[B.S.]

So on a Debian Jessie machine, I'm trying to get system notification 
mail messages out to real e-mail so I actually find out something 
happened. Like an unattended-upgrade failure.

I understand that default installs auto install localhost mail 
facilities only. So I've installed msmtp and it's largely entirely working.

However, e-mail to gmail accounts never seem to land. @live.ca just 
works, instantly even. Yahoo and another non-gmail provider too.

In all cases, cpanel2.indieserve.net swallows up the message without error.

Just nothing ever arrives when sent to @gmail.com.

Anyone have any ideas?

Or is this something needing configuration on mail.kwlug.org, like DKIM, 
or some other bizarreness?

Thanks for any thoughts.