Migrating from qmail server, invalid option "o" in dsync

[Justin Coleman]

Hi folks,
I have an old server running qmail with several years of mails in maildir
format I want to migrate to a new server, without requiring fresh client
download of everything.

Old server is debian 6(?). Local IP is 192.168.0.1.
New server is Debian 10, local IP is 192.168.0.25.

I have dovecot 2.3.4.1 (latest from apt stable) installed and apparently
working - if I manually copy the home directory for my account, I can
connect (using thunderbird) and I get all the emails appearing as new,
forcing redownload. Seems like the new config is at least functional.

I'm trying to follow the migration guide at
https://wiki2.dovecot.org/Migration/Dsync, but I am getting an error
message:
root at newserver:~# doveadm backup -R -u _user_ -o pop3c_user=_user_ -o
pop3c_password=_password_
backup: invalid option -- 'o'
doveadm backup [-u <user>|-A] [-S <socket_path>]  [-fPRU] [-l <secs>] [-r
<rawlog path>] [-m <mailbox>] [-g <mailbox_guid>] [-n <namespace> | -N] [-x
<exclude>] [-s <state>] [-t <start date>] -d|<dest>

Have tried this a couple different ways and according to everything i can
find -o should be valid. Can anyone tell me what I'm doing wrong here?

Thanks!

# 2.3.4.1 (f79e8e7e4): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.5.4 ()
# OS: Linux 4.19.0-9-amd64 x86_64 Debian 10.4
# Hostname: newserver.domain.com
disable_plaintext_auth = no
mail_location = maildir:~/Maildir
mail_privileged_group = mail
namespace {
  hidden = yes
  list = no
  location = pop3c:
  prefix = POP3-MIGRATION-NS/
}
namespace inbox {
  inbox = yes
  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 {
  pop3_migration_mailbox = POP3-MIGRATION-NS/INBOX
}
pop3_uidl_format = %f
pop3c_host = 192.168.0.1
protocols = " imap pop3"
ssl = no
ssl_cert = </etc/dovecot/private/dovecot.pem
ssl_client_ca_dir = /etc/ssl/certs
ssl_dh = # hidden, use -P to show it
ssl_key = # hidden, use -P to show it
userdb {
  driver = passwd
}
protocol doveadm {
  mail_plugins = " pop3_migration"
}
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