When to include a physical address

One of the requirements to be CAN-SPAM compliant is to include a physical address within every promotional email that is sent. If your company hires a third party to send email on your behalf, your physical address should be clearly visible within the message when the message is selling your products and services. There is a stipulation that if your message is transactional or a relationship message, then it does not need to adhere to the CAN-SPAM requirements by including your physical address or unsubscribe link.
Examples of transactional mail would be welcome emails, password resets, auto-responders, shipment notifications, or account alerts.  While you and I may know that these emails aren’t required to include this information most users would not know.
The CAN-SPAM Act has been in effect going on 12 years and recipients look for unsubscribe links and physical addresses within the messages. Emails that are missing this bit of information leads the recipient to believing the message is spam.  While including the physical address and unsubscribe link are not required for your transactional emails, it’s better to be safe than sorry and include them anyways.
The recipient may have recently received a series of marketing emails from you and when they receive a transactional mail message, they may want to adjust the frequency of the mail they are receiving. By not including an unsubscribe link and physical address, the user may resort to marking the message as spam.
When sending marketing and transactional emails, you want to adhere to the law and then take the user behavior and expectations into consideration. There is no harm in including your physical address in both your marketing emails and transactional emails.