I am starting to see that e-mail may cause just as many interruptions to productivity to unapproved data stores (excel spreadsheets, silo databases, etc.)

I was reading an article that offered the following insight

“However, Basex proposed several steps to mitigate information overload. With e-mail as the biggest offender, Basex said users can save time by not e-mailing someone, and then following up with a phone call or an instant message two seconds later [Or, walk to your office 4 seconds later and ask “did you get my e-mail”] (a no-brainer perhaps, but a trap many of us fall into).

Basex also said users must not combine multiple topics or requests in a single e-mail; make sure the subject clearly reflects the topic and urgency of the message; read their e-mails before sending to make sure they make sense; and will not hit reply-all unless necessary or [not] reply with one-word e-mails such as "thanks."

This Dilbert comic seems to offer a similar conclusion.

Another company I’ve been looking at called ActionMethod offers similar insight:

Email can kill productivity, because the actions you must take get buried in regular communication. Tasks should have an ecosystem of their own.

It suffices to say that the issue warrants a deeper study which should result in proper workplace policy for the use of e-mail and collaborative tools (SharePoint, etc.).