This trivial example does not illustrate the usefulness of OO design. Extending the example imagine the requirement is that the target of an email may be either a single user or a group of users, and in addition, email filters can be configured for both individual users and groups of users

Leading to an OO class design roughly like this: (there are other possible OO designs, but this illustrates the point)

// Send an email to a specific user or a group of user taking into account both user and group level filters.

sendEmail(Email, EmailDestination)

class Email {Title, Body, Attachments}

interface EmailDestination {

   Iterator<User> getRecipients(Email); 
   List<Filter> getFilters();

}

class Group implements EmailDestination {

   // returns group filters
   List<Filters> getFilters();                 
   List<User> getMembers();

   // returns all recipients after applying group and 
   // individual recipient filters
   List<User> getRecipients(Email);  

}

class User implements EmailDestination {

   // returns user specific filters.
   List<Filters> getFilters();                          

   // returns itself unless filtered
   Iterator<User> getRecipients(Email);   

}

how would this look with a procedural design?