[exim] Can't use fqdn with user ID for Smtp authentication

Hi,

I encountered an inconsistency problem.
User login cyrus server must use fqdn with user id login (eg.
user@???) and it does so successfully.
When sending email, I only able to authenticate with auth smtp by user
name without domian name.
Trying fqdn with domain name for smtp authtenticaiton results
"fixed_login authenticator failed".

The Authenticaiton of Exim (4.4) is configured as follow:
fixed_login:
        driver = plaintext
        public_name = LOGIN
        server_prompts = UserName:: : Password::
        server_condition = ${if saslauthd{{$1}{$2}}{1}{0}}
        server_set_id = $1

plain:
        driver = plaintext
        public_name = PLAIN
        server_condition = ${if saslauthd{{$2}{$3}}{1}{0}}
        server_set_id = $2

The error from mainlog is:
plain authenticator failed for ([192.168.4.235]) [192.168.4.235]: 535
Incorrect authentication data (set_id=adam.wonder@???)
fixed_login authenticator failed for ([192.168.4.235]) [192.168.4.235]:
535 Incorrect authentication data (set_id=adam.wonder@???)

I think this is problem with Exim configuration. I don't know where the
configure file need to be changed.

Does anyone have any suggestion?

Thanks
Sam