New IP for Server with Reverse DNS

Once we set up the new IP address and Reverse DNS via the hosting control panel, we were supposed to set up signing emails with dkim like
https://hnsws.blogspot.in/2009/05/signing-emails-with-dkim.html

apt-get install dkim-filter
error'd out with 
Unable to locate package dkim-filter

Looking around,
https://askubuntu.com/questions/116553/what-package-replaces-dkim-filter-in-12-04
Opendkim is what was needed - 
https://www.exratione.com/2014/07/setting-up-spf-and-dkim-for-an-ubuntu-1404-mail-server/