It is very important for your marketing mailing list campaign that you know the audience, which you plan to target. A good list should have the mailing list details of only those prospects or existing consumers, who can be approached, if need arises. Updated information - A redundant list would do no good; it would cost you dearly mailing list and might have a negative impact on your marketing campaign.
Always look out for a list that has been mailing list recently updated; generally, such a list would comprise the details of those consumers, who have made a purchase in the recent past, say 10-15 days back or so. Credentials of the vendor/provider - Well, if you mailing list do not wish to waste your hard-earned money, it is very important that you buy the list from a reputed vendor.
It is also advisable that you check if the vendor is a member of the DMA (Direct Marketing Association) or not. If you take care of the aforementioned factors and buy a suitable list, it would be very easy for you to foray into unexplored domains mailing list and outperform your competitors. However, it is highly recommended that you use the mailing lists in combination with other marketing tools, as doing so would really help you in achieving the desired results.