[exim] Exim 4.92 local address qualification problem

I have exim 4.92-8+deb10u3 installed on a Raspberry Pi, configured, I
believe, identically to another RasPi with 4.84.2-2+deb8u6, which is
working as expected. On both systems "exim -bt username" shows :

R: smarthost for username@???
username@???
  router = smarthost, transport = remote_smtp_smarthost
  host mydomain.com [xxx.xxx.xxx.xxx] port=587

However, on the 4.92 system when sending mail from "username" the "from"
address is still the unqualified "username@hostname" instead of
"username@???", so sender verification fails. I haven't been
able to find the difference between the configurations. Adding
"-fFrom:username@???" to the "mail" command works.

/usr/exim4/update-exim4.conf.conf, /etc/mailname ("mydomain.com"),
/etc/email-addresses (empty), /etc/hosts (except for hostname e.g.
raspi1 vs raspi2) are identical and /var/lib/exim4/config.autogenerated
was generated as evidenced by the "exim -bt" output.

I must not be using "exim -d+all -bdf" right; I'm not seeing any output
after "Listening..." when I send test messages.

What am I missing or where else should I be looking for a difference
between the configurations to get the newer installation to qualify the
local address properly? Thanks in advance.