What are the advantages and disadvantages of an email program (such as Eudora or Outlook) that automatically applies and removes protection to email messages between sender and receiver?

What will be an ideal response?

The protection is automatic, that is, it is always applied. But the protection is under control of the package, not the user. And there is no way to tell whether the intended recipient supplied the key or it was retained by the mail handler. Also, there is no way to avoid the overhead.