[Mailman-Users] digest message count

[admin]

Hi,

I am seeing some mail lists handled by mailman with a message count in the
subject line accompanying the digest message.  My digest mailings do not have
these details.  How do I add them?

Here is an example of the subject:
<listname> digest, Vol 1 #2186 - 13 msgs 
                                 ^^^^^^^^
                                 message count

- Noah