[keithg]

The reason email usage is so ubiquitous is because everyone has an email address, and the protocols are well-known and universal.

How else would you propose inviting people to a meeting? Put a paper memo in their mailbox asking for a written reply? Call everyone individually on the phone? Walk around the office and gather everyone together?

If you're thinking about the meeting problem, do you propose a meeting/calendar app/client or protocol that is separate from email? Then the problem becomes saturating your user community with your new client. What do you do if someone doesn't use your new meeting/calendar app/client?

I think what you are describing is a problem with meeting/calendars not email.

[hpaavola]

Because meetings and finding those email addresses are done through email clients, you need to take those into account if you try to write new email client.

Because there isn't any other way to send those invites, figure out the meeting room and the recipients, you need to support those use cases also. Otherwise people will not user your client because then they would have to keep using the old one also.