Yes, you can send tasks via email to someone else's account, but to do so, you need the unique email address of their project you'd like to send tasks to and they must add your email address (the one you'll use for sending these messages) on their list of accepted addresses (this can be done at the bottom of the popup window that shows the unique email address).
Also, if you're working in a team, feel free to try out team-based projects management tool https://wedoist.com which allows inviting people to projects, assigning tasks directly to them, sharing updates, uploading documents and much more.
Thankyou, however i do not understand what you mean by the pop up menu. can you please explain
Please take a look at this short screencast video: http://screencast.com/t/SM3GTGhsTY
As you see, clicking on the gear icon at the top of a task list shows a drop-down menu with "Email tasks to this project" as one of the options. If you choose this option a popup will appear containing the unique email address of this project (where you can send tasks to), detailed instructions on how this feature works and at the bottom - a place to add different email addresses from which Todoist will accept incoming tasks.
If you want to send a task via email to someone else's Todoist account, you must know the unique email address of their project (found in the "Email tasks to this project" popup) and the person that should receive these tasks must add your email address (the one you're going to send these tasks from) on heir Todoist account (at the bottom of this popup).