One of the questions I get asked most often is 'where can I buy a reliable list of email addresses?' I have only one answer: don't even go there.

When you're just starting to build your list, you may not have email addressses for all your customers, let alone prospects. It's tempting to go down the traditional route of buying in a list - after all, it's a standard direct marketing tactic. But there can be problems with this, for example:

• Email addresses frequently change. If the addresses are over 6 months old and haven't been mailed to in that time then you should question the value of the list.
• List brokers rarely have individual email addresses on their books - so you may get a list of names and job titles but with generic email addresses (sales@, info@ etc). Delivery to these kinds of addresses often results in your email never reaching the intended recipient.
• Email list brokers should be able to demonstrate the provenance of email addresses. How were they obtained? What did these people actually opt in to receive? Beware that if the list broker has no audit trail to speak of, in the case of a spam complaint you may be in a difficult position.
• Who else has purchased these addresses and emailed them? If they have been re-sold too often or to the wrong kinds of customer that will negatively affect your campaign and may associate you with spammers.
• If you are planning to email private individuals with whom you have no 'prior commercial relationship' then you are almost certainly contravening the UK Privacy and Electronic Communications legislation (if your target recipients are outside of the UK then check the legislation in the relevant market). The Website of the Information Commissioner's Office has useful guidance notes on how to interpret the rules at http://www.informationcommissioner.gov.uk/eventual.aspx?id=96