Utilizing SMTP AUTH (6)
Lookup PLAIN

auth_advertise_hosts = ${if eq{$tls_cipher}{}{}{*}}

begin authenticators

plain_file_server:
   driver = plaintext
   public_name = PLAIN
  server_condition = "${if crypteq{$3}{${extract{1}{:}{${lookup{$2}lsearch{/usr/local/etc/exim/authplain}{$value}{*:*}}}}}{1}{0}}"
   server_set_id = $2
   server_prompts = :