To be CAN-SPAM compliant, you need to adhere to the following guidelines set by Federal Trade Commission (FTC) for B2B organizations:
Don't use false or misleading header information. Your "From," "To," "Reply-To," and routing information - including the originating domain name and email address - must be accurate and identify the person or business who initiated the message.
Don't use deceptive subject lines. The subject line must accurately reflect the content of the message.
Identify the message as an ad. The law gives you a lot of leeway in how to do this, but you must disclose clearly and conspicuously that your message is an advertisement.
Tell recipients where you're located. Your message must include your valid physical postal address. This can be your current street address, a post office box you've registered with the U.S. Postal Service, or a private mailbox you've registered with a commercial mail receiving agency established under Postal Service regulations.
Tell recipients how to opt out of receiving future email from you. Your message must include a clear and conspicuous explanation of how the recipient can opt out of getting email from you in the future. Craft the notice in a way that's easy for an ordinary person to recognize, read, and understand. Creative use of type size, color, and location can improve clarity. Give a return email address or another easy Internet-based way to allow people to communicate their choice to you. You may create a menu to allow a recipient to opt out of certain types of messages, but you must include the option to stop all commercial messages from you. Make sure your spam filter doesn't block these opt-out requests.
Honor opt-out requests promptly. Any opt-out mechanism you offer must be able to process opt-out requests for at least 30 days after you send your message. You must honor a recipient's opt-out request within 10 business days. You can't charge a fee, require the recipient to give you any personally identifying information beyond an email address, or make the recipient take any step other than sending a reply email or visiting a single page on an Internet website as a condition for honoring an opt-out request. Once people have told you they don't want to receive more messages from you, you can't sell or transfer their email addresses, even in the form of a mailing list. The only exception is that you may transfer the addresses to a company you've hired to help you comply with the CAN-SPAM Act.
Monitor what others are doing on your behalf. The law makes clear that even if you hire another company to handle your email marketing, you can't contract away your legal responsibility to comply with the law. Both the company whose product is promoted in the message and the company that actually sends the message may be held legally responsible.
Source: https://www.ftc.gov/tips-advice/business-center/guidance/can-spam-act-compliance-guide-business