Bnews reply problem

[Super user]

I recently installed Bnews on my SCO XENIX 2.3.2 system. My problem is that
when I reply to a message it comes up with the 'append .signature file [y]'
prompt. After I say yes it comes up with something like:

Can't open directory/file: /bin/mail

I can post messages without any problem. 

Eric