Guidelines for permission based email marketing
Sending people unsolicited email, commercial or otherwise, is against the law in many countries worldwide. Besides that, wouldn't you rather be talking to people who you know are interested in what you have to say?
Who can I send email to?
People who have specifically signed up through your website
They ticked a checkbox (not one checked by default) on your signup or sales form
People who completed offline forms & indicated they wanted to be emailed
They filled in a form where they specifically agreed to receive email
People who gave you their business card and asked to receive email
They gave you a business card and you explained to that you will be in touch by email
They purchased something off you in the last 2 years
By making a purchase from you they have provided their permission implicitly, although it is much better to explicitly ask them.
Lists or email addresses received from a third party
Includes any list you bought or rented, got from a partner or membership
organization. No matter the claims of the source of this list, you cannot send email to them.
Addresses you collected or "copy & pasted" from the Internet
Even if they look like ideal customers for you, you can't email someone just
because you found their address.
Addresses you haven't emailed in the last 2 years
Permission doesn't age well. Even if you got their permission legitimately, they won't remember giving it to you. If you haven't sent something to that address in the last 2 years, you can't start now.