[Dovecot] %d is empty in mail_location

I have this in dovecot-postfix.conf:

mail_location = maildir:/home/mail/dnamesum=%12MLd/dname=%Ld/unamesum=%12MLn/uname=%Ln/mail

Yes, it is excessive, but that's just for testing. The pattern I really want is less clear for debugging. In postfix/main.cf I have:

mailbox_command = /usr/lib/dovecot/deliver -c /etc/dovecot/dovecot-postfix.conf -a "${RECIPIENT}"

I verified through strace that -a "${RECIPIENT}" is in fact getting a full user@domain address. The problem is that %d and %Ld are coming up as empty, and %12MLd is giving me the first 12 hex characters of an md5 of an empty content. It's losing the domain name somewhere. It's in the mail headers and in the -a option. So what else is needed?