[Exim] TLS errors from remote host

Hello,

First, I want to say Philip, you've really done a fantastic job with
the Exim book. Most O'Reilly books are quite good but this is one of
the best for usefulness, clarity and readability. Thanks!

Okay, there's a host that one of my customers has mailed before and now
all her mails are being rejected. I had a look at some exim -d9 -qff
output and here's some of it:

delivering 15SLJN-00052U-00 to mail.icehouse.net [204.203.53.2] 
(jjustice@???)
set_process_info: 31293 delivering 15SLJN-00052U-00 to 
mail.icehouse.net [204.203.53.2] (jjustice@???)
Connecting to mail.icehouse.net [204.203.53.2.25] ... connected
read response data: size=29
   SMTP<< 220 mail.icehouse.net ESMTP
   SMTP>> EHLO mx1.overland.net
read response data: size=79
   SMTP<< 250-mail.icehouse.net
          250-PIPELINING
          250-STARTTLS
          250-SIZE 0
          250 8BITMIME
host in ? no (option unset)
   SMTP>> STARTTLS
read response data: size=57
   SMTP<< 454 TLS not available: missing RSA private key (#4.3.0)
ok=0 send_quit=1 send_rset=1 continue_more=0 yield=1 
first_address=541008
   SMTP>> QUIT
set_process_info: 31293 delivering 15SLJN-00052U-00: just tried 
mail.icehouse.net [204.203.53.2] for jjustice@???: result 
DEFER
LOG: 0 MAIN
   SMTP error from remote mailer after STARTTLS: host mail.icehouse.net 
[204.203.53.2]: 454 TLS not available: missing RSA private key (#4.3.0)

Okay, although I built in TLS support for exim and have generated a
key, I've not set anything up for TLS on our side; nothing is being
advertised or broadcast.

I don't see this error from any other host and just want to be clear on
what's going on here: is icehouse.net insisting on TLS to complete the
delivery or is my server doing something I didn't think I was telling
it to do?

Thanks again,
Todd