Error from client:
  java.net.SocketException: The connection was reset

Extract from /var/log/exim/exim_main.log:

2011-10-08 11:53:33 TLS error on connection from genld-224-049.t-mobile.co.uk ([10.217.135.147])
 [149.254.224.49] (SSL_accept): error:00000000:lib(0):func(0):reason(0)
2011-10-08 11:53:33 TLS client disconnected cleanly (rejected our certificate?)