It took some time, but I finally found an answer to the question I posted. If anyone else is having the same problem, the solution is to set "receiver_verify = true" in /etc/exim.conf. Exim will then return a 550 status to the RCPT TO command in the following example.
John Kuhn wrote: > telnet badhost.corp.com 25 > Trying... > Connected to badhost.corp.com. > Escape character is '^]'. > 220 badhost.corp.com ESMTP Exim 3.12 #1 Thu, 09 Mar 2000 14:45:18 -0500 > MAIL FROM:<[EMAIL PROTECTED]> > 250 <[EMAIL PROTECTED]> is syntactically correct > RCPT TO:<"[EMAIL PROTECTED]"@[192.1.1.1]> > 250 <"[EMAIL PROTECTED]"@[192.1.1.1]> is syntactically correct