As root, open Email Notifications. There's one template per phase, with a live preview using sample accounts and dates.
Placeholders you can use:
[CPANEL_RESELLER_USERNAME]: the reseller's name[ACCOUNTS]: the list of affected accounts[DATE_AUTO_SUSPENSION]and[DATE_AUTO_REMOVE]: the dates[COMPANY_NAME],[HOSTNAME]and[WHM_URL]
Branding sets the company name, logo URL (https), accent colour and footer note for every template. Use Send test to email yourself before saving.
