I found a fix, from this webpage "Update Verizon.net account info in POP3 email applications":
This page is dated April 13, 2018, and it tells me to simply change my Outlook email settings as follows:
incoming mail server to pop.verizon.net (had been incoming.verizon.net)
outgoing mail server to smtp.verizon.net (had been outgoing.verizon.net)
Did that, and everything is now back to normal.