Emails are a mighty tool when it comes to communication and marketing, but they are not free of dangers. Spam - real spam or perceived spam - is serious business.
The safest way is to send informative mailings only to recipients that requested them. If a customer subscribes to your newsletter at first, but rescinds his subscription later, you should be careful: sending out one more email to him might result in a cease-and-desist order, fines and even costly lawsuits.
How can I make sure I don't send out spam-emails?
For business newsletters and mail blasts we recommend using a professional email marketing software. Every software worth its money will enable you to create email blacklists and exclude all addresses on those lists from sending processes. This way you can easily respect de-registration.
But what if an email is sent out directly from my usual email software, e.g. via MS Outlook?
In this case a simple rule in the Exchange Server Toolbox rule system will keep you safe from angry customers and their trial-hungry lawyers. The rules apply to all emails leaving your server, you do not have to set them for every single sender.
Once a customer informs you that no further communication via email is desired, you simply add the address or even the entire domain name (complete or partly) to the blacklist in the corresponding rule. If one of your employees tries to send an email to an address matching the internal list, the email will not be sent and Exchange Server Toolbox informs the sender about the reasons.
This way you make sure that no undesired email leaves your company.
The company John Doe's CarWash has informed you that any further email will be counted as spam. You don't want to risk a lawsuit and make sure that no mail will reach the company and use the rule to blacklist all email addresses containing @john-does-carwash.net (i.e. the entire domain). To inform your employees you formulate an autoreply: "The recipient does not wish to receive emails from us. The email was not sent."