Guest Account without account

Is there any way we can enable guest account at our website that way people can post without having accounts?
at the same time, all the posts must be sent to moderation for approval.

Nope, not through the web interface. However, you can set up a category to receive mail sent to an email address, which creates staging users for folks mailing in, and as it is a category all the normal security/moderation tools are available.

Look up:

  • staged users
  • category moderation
  • new topic by email