Multitask or single task

The problem: email, blackboard, updating, checking in, and how it morphs into too much time without much productivity/output. Strictly limit time spent on email/online?  Or respond a different way to tasks that appear through those media? If it isn't in my list, I don't do it?  but I'm already here?  Why not just get it done?  But is it really necessary?  Here is a quote that haunts me a bit, and my quicky translation: One often suffers from the fact that one has a great deal of work, but no identified mission (to which the work belongs)

"Häufig leidet man daran, dass man zwar viel Arbeit, aber keine Aufgabe hat."

Dr. phil. Hellmut Walters