argonid and dovecote

[Jerry]

on a FreeBSD 11.2 amd64 machine, I am trying to get Dovecot 2.3.4 to play
nice with "argonid" encryption.

In the "10-auth.conf" file, I tried:

auth_mechanisms = plain argon2id

Upon restarting dovecot, I received an error message when attempting to
actually it:

auth: FATAL: Unknown authentication mechanism "ARGON2ID"

Output from doveadm pw -l

doveadm pw -l
SHA1 SSHA512 BLF-CRYPT PLAIN HMAC-MD5 OTP SHA512 SHA RPA DES-CRYPT CRYPT SSHA
MD5-CRYPT SKEY PLAIN-MD4 PLAIN-MD5 SCRAM-SHA-1 LANMAN SHA512-CRYPT CLEAR
CLEARTEXT ARGON2I ARGON2ID SSHA256 NTLM MD5 PBKDF2 SHA256 CRAM-MD5
PLAIN-TRUNC SHA256-CRYPT SMD5 DIGEST-MD5 LDAP-MD5

I assume I am making a stupid mistake, but I do not know what it is.

-- 
Jerry