[exim] Client Authentication

I'm working on a mail client and I'm having some trouble with PLAIN
authentication and Exim. With other servers, like Postfix for
example, the client says EHLO and gets a list of authentication
schemes, among other useful info. With Postfix my client can send
AUTH LOGIN PLAIN\n and the sever asks for a b64 user name. Then the
client sends the b64 user name, gets a request for a password, it
sends the b64 password and then the authentication is either excepted
or rejected.

When I try to do this with an Exim server it immediately says
"Invalid base64 data" Here's a transcript with the names changed to
protect the innocent:


telnet mail.foo.com 25Trying xxx.xxx.xxx.xxx...
Connected to mail.foo.com.
Escape character is '^]'.
220 mail.foo.com ESMTP Exim 3.36 #1 Thu, 02 Jun 2005 23:05:22 +0100
EHLO [10.0.0.1]
250-mail.foo.com Hello client.bar.com [xxx.xxx.xxx.xxx]
250-SIZE 5242880
250-PIPELINING
250-AUTH PLAIN LOGIN
250-STARTTLS
250 HELP
AUTH PLAIN LOGIN
501 Invalid base64 data

I know that the account works because I can use other mail clients to
authenticate.

Can someone tell me what Exim is expecting ? I also tried some
variations of encoding the username and password. I found a perl
script that will make a \0user\0password b64 string and sent that
along with the AUTH PLAIN LOGIN but get the same results.

Any help would be greatly appreciated.

Matt