Eric Schmidt's aspects of e-mail not in Twitter

In Google CEO Eric Schmidt's comments about twitter he highlights some aspects of the e-mail system that twitter lacks.

The aspects of e-mail he mentions are:

• storage
• revocation
• identity

Could anyone explain these aspects of the traditional e-mail system? I'm interested in creating a twitter-like system and would like to better understand existing communication protocols and their abilities/characteristics.

From stackoverflow

• Since after 6 hrs. no one has answered this I'll give it a try.

  • storage

  Well you can't store your tweets the same way you can store your e-mail, do you?

  • revocation

  Mmhh, perhaps because in an e-mail you can take back some comment or discuss back and forward about some topic keeping the thread in one place.

  • identity

    The email identifies you as a user in a domain ( user@domain ) hence creates an on line identity. Twitter does not ( at least yet )

  Twitter didn't include these kind of features because its nature was well, not being an e-mail susbtitute.

  web-forums ( like this ) also evolved from the e-mail system, where all the questions/answers use the e-mail as communication channel.

  Rex M : I don't know about the identity one. rexm@twitter is as globally unique as rex@rexmorgan.net. Just one is more commonly accepted.

  Daniel Gill : For storage, on twitter one can still see the history of their tweets, no? Interesting take on revocation. And I would agree with Rex's idea of on-line identity.

  OscarRyz : @Daniel: Not like in e-mail ( at least not like gmail :P ) @Both: On the identity, I don't know my self either. I move from Yahoo to gmail once, so I was not so tied to the e-mail after all. But definitely my work e-mail and my friends e-mail are used as my web identity. Only time will tell