database design for multiple and all pepople
Mail Master table

MailID (PK)
Mail content 

Emp Master table

EmpID (PK)
EmpName


Mail-Employee Mapping table

Mail-Employee_ID (auto increament id PK)
MailID (FK)
EmployeeID (FK)

Group_Master table

GroupID (auto increament PK)
GroupName 

Group_Employee_Mapping table

Group_Employee_ID (auto increament)
GroupID (FK)
EmployeeID (FK)
(GroupID+Employee are unique so Composite PK)


I think tables and their roles are self explanatory.

Some rule for Group Master:-

Group_Employee_Mapping is predefined in system :you have already mapped all employee and its group in this table.One employee can belong to many group .

If Group='All' don't store "All" employee in Group_Employee_Mapping Table.As this is unnecessary

If user select "All" select all employee from Employee Table ,send them mail and store each employee and mailid in "Mail-Employee Mapping" table

If user select any specific group then select those employee from Group_Employee_Mapping table,send them mail and store them in Mail-Employee Mapping