namespace configuration error

I've got a few errors I'm trying to track down, probably all related...

Aug 15 14:03:14 xyzzy dovecot: imap-login: Login: user=<jeff>, method=PLAIN, rip=100.8.22.62, lip=132.238.254.34, mpid=4803, TLS, session= Aug 15 14:03:14 xyzzy dovecot: imap(jeff): Error: namespace configuration error: Duplicate namespace prefix: "" Aug 15 14:03:14 xyzzy dovecot: imap(jeff): namespace configuration error: Duplicate namespace prefix: "" in=0 out=357 Aug 15 14:03:15 xyzzy dovecot: imap-login: Login: user=<jeff>, method=PLAIN, rip=100.8.22.62, lip=132.238.254.34, mpid=4806, TLS, session= Aug 15 14:03:15 xyzzy dovecot: imap(jeff): Error: namespace configuration error: Duplicate namespace prefix: "" Aug 15 14:03:15 xyzzy dovecot: imap(jeff): namespace configuration error: Duplicate namespace prefix: "" in=0 out=357 Aug 15 14:04:51 xyzzy dovecot: lda(jeff): Error: User initialization failed: namespace configuration error: Duplicate namespace prefix: "" Aug 15 14:04:51 xyzzy dovecot: lda: Fatal: Invalid user settings. Refer to server log for more information.

# dovecot -n # 2.2.31 (65cde28): /etc/dovecot/dovecot.conf # OS: Linux 4.12.5-300.fc26.x86_64 x86_64 Fedora release 26 (Twenty Six) ext4 mail_location = mbox:/home/%u/mail:INBOX=/home/%u/mbox mail_plugins = snarf zlib mbox_write_locks = fcntl namespace Snarf { hidden = yes list = no location = mbox:/home/%u/mbox:INBOX=/var/spool/mail/%u:INDEX=MEMORY prefix = ~~Snarfbox/ separator = / } namespace default { inbox = yes location = prefix = separator = / } namespace inbox { location = mailbox Drafts { special_use = \Drafts } mailbox Junk { special_use = \Junk } mailbox Sent { special_use = \Sent } mailbox "Sent Messages" { special_use = \Sent } mailbox Trash { special_use = \Trash } prefix = } passdb { driver = pam } plugin { mail_log_events = delete undelete expunge copy mailbox_delete mailbox_rename mbox_snarf = /home/%u/mbox snarf = ~~Snarfbox/INBOX } protocols = imap pop3 service imap-login { inet_listener imap { address = localhost } } service pop3-login { inet_listener pop3 { address = localhost } } service postlogin { executable = script-login -d rawlog } ssl_cert =