It’s my personal opinion; anybody who needs to keep in touch with their clients must visit the site << url snipped >> because it provides an application to sends out thousands of mails in MX mode and works like a mail server and also provides exciting built-in e-mail templates. Moreover, it also provides an Unsubscribe link to clients so that in case some of your targeted customers are not interested in receiving the mails, they can just click on the Unsubscribe Link.

Nonono, bulk e-mail is definitely not a good idea. Many people mistakingly feel that if they can get their word out to the masses, people will visit their site. The problem is that most people feel that businesses who resort to spamming tactics to generate traffic almost always aren't businesses worth their time or money. It really gives a negative opinion, IMO.

Sending out e-mail to prior clients is another story. It must still be done very tactfully and very tastefully and, of course, as rossbliss said, provide an unsubscribe link. Opt-in lists are the best.