[exim] smtp_banner refuses to be renamed

I have a very simple update-exim4.conf.conf file runing on debian 6.

Since I'm just starting out I'm experimenting with various features to
learn.

I've inserted the following as a test in the main section of the
configuration file:

dc_smtp_banner="$primary_hostname Microsoft ESMTP MAIL Service, Version:
5.0.2195.6713 ready at $tod_full"

I've also tried:

dc_smtp_banner = "testing banner message"

I've restarted exim4 with each test.

When I telnet into localhost 25 I still see:

221 name_of_my_domain ESMTP Exim 4.72 Mon, 16 May 2011 22:47:50 -0400

what am I doing wrong?

Thanks.