How to offer tls only on certain ports?

   How can I setup exim to only offer tls on certain ports?  For example,
   if I only want to offer tls on ports 25 and 587 for all hosts then I
   thought that I could set tls_advertise_hosts as follows:
       tls_advertise_hosts = 0.0.0.0.25 : 0.0.0.0..587
   However, it does not appear to work. Any help would be appreciated!
   Thanks,
   Gordon
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