[exim] Bad Address Syntax

Wondering what this means:

220 v185.mailsnare.net ESMTP
helo ctyme.com
250 mail.mailsnare.net
mail from:<>
250 Ok
rcpt to:xxx@???
501 Bad address syntax
rcpt to:<xxx@???>
250 Ok

If I present the email address in <> it works but without the <> it
doesn't. What causes this?