Courier certificate

[richard@the-place.net]

Every time I log on to IMAP server via mutt, it says

This certificate belongs to:
   localhost  postmaster@example.com
   Courier Mail Server
   Automatically-generated IMAP SSL key
   New York  NY  US

This certificate was issued by:
   localhost  postmaster@example.com
   Courier Mail Server
   Automatically-generated IMAP SSL key
   New York  NY  US
...
WARNING: Server hostname does not match certificate

I assume this is a default certificate generated by Courier at install.  I
have so far failed to find out how to replace it with a "correct
certificate"

Can anyone point me at the relevant instructions, please?

-- 
richard