While email marketing is still viable, it is not as highly regarded as in the past. What seems to work most effectively is group/mail/newsletter types for users who actually OPT IN for same. If your widget is that cool, they'll gladly receive in their inbox. If not, then junk filters will be applied and your widget site/letter will get a black eye. And might even rise to the level of spamhaus type isp filters. So keep that in mind, too.

Initially you need to take a database of all the email IDs you want to send. Next, you need to plan a email marketing campaign. The next step is to professional messages in the email. The content should be relevant to the message you are to convey. It should be easily understandable to the recipient.

Email marketing can be dangerous because of many different reasons. First of all, people did not required to receive emails (if you bought an email list)so they will mark the emails as spam and soon your email service provider may disallow you to use email on the future by not sending your emails.

If you want to build a good marketing campaign through email must beware of many side effects.

The key is building the email list with the right kind of people. I build my list through my website so those people are interested in my product and conversion rates are high.

Agree with runbch. But question comes: how to reach the right kind of people? Usually what I do is call the targeted potential customer and have a nice talk, reach the right man/woman's and ask their email politely. then follow. This would be more effective.

The secret to successful email marketing is by know your target audience. Extensive research is needed here and the use of professional messages (preferably unique per message) is also an additional factor.