Digital ID If you want to send your email with Digital ID and provide encryption for the email content. You need to purchase the digital ID from below site: Symantec Digital ID Purchase It will cost $25 per year https://www.ablebits.com/office-addins-blog/2014/04/11/email-encryption-outlook/
Read more
Office 365 Subscription
Microsoft Office 365 Office 365 Business Essentials $5 (Mail box only) Office 365 Business $8.25 (Office desktop software only) Office 365 Business Premium $12.5 (Mail box and Office desktop software) https://products.office.com/en-us/business/compare-office-365-for-business-plans
Read more