I wouldn't have thought buying lists of peoples emails to send campaigns to is the best (or legit?) option?
Yes and No!! Many consumer data suppliers have invested time and effort in building a pool of fully opted-in individuals that have specifically given their permission to receive marketing information by email on third party offers. These lists are then made available on a 'rental' basis with the broadcast being undertaken by the consumer data supplier on their chosen broadcast platform. In short the email addresses are not released to the end-user! In this way consumer data suppliers remain fully compliant since every record holds the date and time stamp and URL where the individual opted-in and any creative sent out carries an unsubscribe message and a declaration of why they are receiving the email, who from and where they would have opted-in.
The benefit of using a professional consumer data supplier is that, as Phil at Shortlist has pointed out, the data can often be segmented further using a wide range of overlays so the the recipients are more likely to be receptive to your product or service maximising the chance for success.
As per your comment, and that of others in this thread, I would be very wary of anybody that is willing to release email addresses en masse for peanuts money!!! The bounce rate will be high and the provenance of the emails questionable and you could land yourself in a wholeheap of trouble under current legislation if you cannot provide valid opt-in details in the event of a data access request. I would recommend dealing only with suppliers that are DMA members as they are bound by the DMA code of practice.
As a channel email can and does work, however, email isn't a strategy in its own right! It should form part of an overall multichannel marketing strategy. With current average open rates of c.1-5% and click throughs of anything from 0.5% updwards you are going to have to work hard to get your message opened which means making sure that there is a strong call to action, an attractive offer, meaningful engagement and a clear and navigable landing page or website at the other end. Although it is certainly important, quality data is just one element of a successful campaign.
I would suggest talking to two or three email providers, listen to their advice and work this into a viable strategy and how likely open/conversion rates fit with your expectation. Once you are satisfied then trial, test and analyse. Start off small scale and minimise your exposure and tweak future campaigns to find a winning formula.
All the best
Adam