@PhilipHeyes
Thank you for the suggestions.
1. DKIM is ON
2. See attached image. Also they resolved mail.enmail.co to 91.204.208.195 and reported that it is not on any blacklists.
3. The only other email address I've got is a gmail one. Looking back, the header of a message that was delivered successfully 2 months ago only mentions SPF and DMARC, not DKIM. This afternoon, I tried again:
a) an email from self@<account>.plus.com to my gmail address arrived after 706 seconds.
b) an email from wife@<account>.plus.com (sent a minute after the first one) arrived after 199 seconds.
Both included DKIM=pass.
I could try to view this as progress in the right direction ... for now.
