Do you often work with external staff such as consultants or freelancers? Since they usually only communicate on behalf of your company for a certain period of time, you can do without additional Microsoft licenses:
Hornet.email is the ideal low-cost solution, which can be easily combined with Microsoft 365 and offers the same AI-based protection mechanisms as 365 Total Protection.
The same applies to employees who do not permanently need the full range of Microsoft 365 functions, as is often the case with warehouse and production employees. By using Hornet.email, they can still be reached under the existing domain in Tenant and are fully protected.