I see. There's no specific source. What I'm looking for is the most general term that would cover all types of bulk correspondence, and could be used for e-mail communication as well.
Spam would be fine in case of negative connotations. What I'm looking for, however, has to be neutral. Imagine, for instance, there's a company that needs to inform its clients of product updates, notify specific groups of customers or business partners of various important changes in services, etc. What term would you use?