I need to track some issues with deleted messages so I have been trying to set up the mail_log plugin.  I have Dovecot v2..27 running on Debian 9.  I have configured /etc/dovecot/conf.d/10-logging.conf, 20-imap.conf, and 20-lmtp.conf and restarted dovecot, but I see so difference in /var/log/mail.info & /var/log/syslog when I delete a message from my Inbox in Roundcube.  Here is the abbreviated output from doveconf -n:

# 2.2.27 (): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.4.16 ()
# OS: Linux 4.9.0-14-amd64 x86_64 Debian 9.13 ext4

plugin {
mail_log_events = delete undelete mailbox_delete mailbox_rename
mail_log_fields = uid box msgid size
sieve = ~/.dovecot.sieve
sieve_after = /etc/dovecot/sieve-after
sieve_dir = ~/sieve
}

protocols = " imap lmtp sieve pop3"

protocol lmtp {
mail_plugins = " sieve notify mail_log"
}

protocol imap {
mail_max_userip_connections = 50
mail_plugins = " notify mail_log"
}

What am I missing?