In order to prevent being labeled a spammer, you need to ensure that your intended recipients have given their consent to receiving an email via some affirmative means, such as a double opt-in procedure.
It is also important that you have procedures in place that allow the recipient to easily revoke their consent i.e. an ‘unsubscribe’ or ‘remove’ link in the mail.
Best Practices to conduct a legitimate mailing list:
Make use of a double opt-in procedure. Not only must the user take action to add himself to a list, but he then receives a confirmation email of his subscription. He must reply to the email to be added to the list. This is done to ensure that the customer did not subscribe by mistake or somebody else did not subscribe him to receive your regular email.
A ‘remove’ or ‘unsubscribe’ link (an opt-out procedure) must be provided to make it easier for the recipient to revoke consent or to terminate their subscription. Mailings must cease promptly once a subscription is terminated.
Mailing list administrators must take adequate steps to ensure that their lists are not used for abusive purposes.
Avoid multiple font sizes and colours as these promote mail being flagged as spam.
Blank spaces increase your spam percentage allocated by most scoring systems.