[exim] SMTP-AUTH problem

Hello,

I have a slight problem, my users are in Ldap, and smtp auth is
working correctly. BUT, we have some code running on remote systems
that we have no access to, trying to supply the username as the full
email address of the account instead of just the givename.

How can I edit my authenticator in exim4 to allow both "user" and "user@???
" as the supplied username?

Here are my current authenticators:

pam_plain:
     driver = plaintext
     public_name = PLAIN
     server_condition = "${if pam{$2:$3}{1}{0}}"
     server_set_id = $2
     server_prompts = :
pam_login:
     driver = plaintext
     public_name = LOGIN
     server_prompts = "Username:: : Password::"
     #server_prompts = :
     server_condition = "${if pam{$1:$2}{1}{0}}"
#   server_condition = "${if or {pam{{extract{1}@}:$2}{1}{0}}}  
{pam{$1:$2}{1}{0}}}"
     server_set_id = $1

Thanks so much,
Ian