ZipLip is a good enough service for anyone who cannot afford their own encryption system, but I do not see it as being anything more grandiose than another Web business with a coolish service designed to increase its site traffic and give ZipLip - irrespective of whatever it says - a database of valuable e-mail addresses.
If you want to send someone a confidential e-mail, you go to the site, click on the compose message link, write your message - filling out the requisite sender and recipient information - and get ZipLip to send it for you.
ZipLip uses Secure Sockets Layer encryption to code the message, but does not actually send it. Instead, it notifies the recipient who then visits the site to read the message, which is supposedly deleted from the ZipLip servers immediately afterwards.
It is also supposed to be deleted if it is unread for 24 hours.
When you compose the message, you supply a password the recipient must enter in order to read the message. This is the biggest flaw in the service.
ZipLip says careless use of passwords is one of the biggest causes of security breaches. But when you use the company's service, you still have to send the password you assigned for the mail to the recipient.