login:
        driver = plaintext
        public_name = LOGIN
        server_prompts = "Username:: : Password::"
        server_condition = ${if pam {$1:$2}{yes}{no}}
        server_set_id = $1
        client_send = : ${extract{username}{$address_data}} : ${extract{password}{$address_data}}

plain:
     driver = plaintext
     public_name = PLAIN
     client_send = "${extract{auth_plain}{${lookup{$host}lsearch{/etc/exim/smtp_users}{$value}fail}}}"