One particular slang term has made its way into the modern dictionary to become a word so officially used - spam. "Don't spam my mail box," has become one of the most common expressions of the internet world. Unfortunately, this was triggered by aggressive email Marketing Campaigns aimed off-target at those who do not subscribe to the products, services, ideas, etc.
Annoyed users complained, on those who sent bulk messages, to their mail servers and ISPs (Internet Service Providers). Even before you begin, just try to understand what falls under spamming and what not. Many of your mail servers have guidelines, terms of conditions, terms of service, etc. on what is called spam.
Major service providers as Yahoo, Rediff, Hotmail, etc. can identify and block spam from reaching your inbox. The problem with it is that bulk email marketing campaign in itself can be called spamming. There is a sigh of relief for internet and online marketers as email promotion is not crime as per the laws of many countries.
People simply mark such promotional messages as spam and send them to the bulk/junk folder. They are quite content with that though they are surely annoyed by the unsolicited messages. Even then, be careful about the law as new cyber laws are created each and every day. Hence, you must take adequate care and attention for your receivers to feel that you send only genuine and innocuous promotional advertisements.
When the laws are made tough, all that you are expected to do is to make your campaign a success by optimizing your content to cater to the needs of your receivers.