Hello Cathy,
That's a good question. I am not claiming this as gospel, but I am going to give you my
personal opinion on the matter.
I recommend AGAINST buying lists of email addresses, for the following reasons:
1) They have not truly requested information from you--they may or may not have requested information from the company that sold you the list
2) Either way, spam complaints tend to be high from purchased email lists
3) You'll have to import them into your autoresponder, and the more reliable autoresponders like Aweber do not allow you to import purchased email lists
4) If you import them anyway, your autoresponder will almost certainly require them to respond to a verification message before sending them any emails. Confirmations tend to be very low and spam complaints tend to be high as a result, which could cause you to be banned by your autoresponder service (I know Aweber can and does ban accounts for this)
Instead of buying emails, I recommend that you build your own opt-in list. One method that is highly effective for this is
Rent-A-List
They are my favorite service for email marketing and list-building. They actually guarantee that you will get a certain number of opens, or they re-run the campaign for you.
In this case, you write the ad copy, but Rent-A-List mails it from their servers, to their list of business-opportunity-seekers who have specifically requested to receive information from Rent-A-List. If they go to your lead capture page and opt-in, then they have also requested information from you and can be considered a high-quality lead.
Hope that helps!