If you have forget to add SPF and DKIM while creating accounts, there is cpanel script available to create SPF and DKIM for existing accounts.

script to enable SPF

Code:
# /usr/local/cpanel/bin/spf_installer $username
Where $username is the account name of your cPanel account
script to enable DKIM

Code:
#  /usr/local/cpanel/bin/dkim_keys_install $username

Where $username is the account name of your cPanel account

To do this in bulk we can use a simple for loop. Use the following script

Code:
# for username in `ls -A /var/cpanel/users` ; do
       /usr/local/cpanel/bin/dkim_keys_install $username  &&
       /usr/local/cpanel/bin/spf_installer $username ; done