However tempting it may seem, just don't go there. We're not just talking here about the dodgy providers who offer millions of addresses for peanuts, but the more professional looking ones who will provide you with a segmented, opt-in list from people who have agreed to receive "3rd party" marketing about your chosen subject.

The main problem here is that the recipients on these lists will not have the slightest clue who you are. No matter what permission they gave to receive "3rd party" mailings they have not given you their permission to email them. Sending mail to these people will have many of them hitting the Report Spam button in their email client and if too many do that your domain is going to end up on spam blacklists. Can you afford for your brand to become blacklisted and have your reputation tarnished?

The next problem is you have no idea when and where the address was collected - it could have been added to the list years ago and may no longer even be in use. Sending email to non-existent or dead addresses will also count against you and you could again end up on one of those blacklists. What's more, if you receive a complaint and are asked to prove where you got the address, which site they opted in on along with date/time/IP address - could you provide that information?

Then you run into the relevancy issue. The recipients who do actually receive your mail, don't report you for spamming and open it up may not even find the content relevant to them (after all they have no idea who you are) - they'll just delete it.

So, you spent all that money on buying/renting a list then money on sending it out only to find most did not arrive, the ones that did weren't opened, you've got a ton of spam complaints and your domain is on a number of blacklists - now it doesn't seem like such a tempting idea after all!

Oh and finally using a purchased/rented list will break the Ts and Cs and anti-spam policies of almost any ESP - us included. So just don't bother - we can see purchased lists a mile off.