该法律将主要目的为广告或推销产品或服务的邮件视为商业邮件。CAN-SPAM 随后对真实的发件人信息、广告标识、邮寄地址和有效的退订机制提出了要求。
联邦贸易委员会 (FTC) 的合规指南是以下要求的来源。关于 Bird 的退订处理，请参阅电子邮件同意与 CAN-SPAM。
它有哪些要求？
七项要求，引用 FTC 的原文：
- Don’t use false or misleading header information.
- 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.
- Tell recipients how to opt out of receiving future marketing email from you.
- Remember that subscribers and members can opt out of marketing emails, too.
- Monitor what others are doing on your behalf.
注意这里没有提到的：法律不要求收件人事先同意接收你的邮件。CAN-SPAM 规范的是你如何发送商业邮件，而不是你是否可以开始发送。
最后一项要求最容易让外包发送的公司感到意外。FTC 明确指出 "even if you hire another company to handle your email marketing, you can’t contract away your legal responsibility to comply with the law"，并且被推广的公司和负责发送的公司都可能被追究责任。
它覆盖我的哪些邮件？
主要目的是商业性质的邮件受该法约束，这是一项判断标准，而不是一个标签。
FTC 将邮件内容分为三类：商业、事务性或关系类、以及其他。纯事务性邮件 "may not contain false or misleading routing information, but is otherwise exempt from most provisions of the CAN-SPAM Act"。纯商业邮件必须满足全部七项要求。混合邮件根据哪种目的占主导来判定：
If a recipient reasonably interpreting the subject line would likely conclude that the message contains an advertisement or promotion for a commercial product or service or if the message’s transactional or relationship content does not appear mainly at the beginning of the message, the primary purpose of the message is commercial.
由此直接得出两条设计规则。促销性的主题行会使邮件被判定为商业邮件，无论正文说了什么。排列顺序也很重要：事务性内容必须放在最前面，而非放在促销内容之后。
什么算事务性邮件？
五个类别，FTC 警告不要做宽泛解读。
- Facilitates, completes, or confirms a commercial transaction that the recipient already has agreed to;
- gives warranty, recall, safety, or security information about a product or service the recipient bought;
- notifies the recipient about a change in the terms or features of a membership, subscription, account, loan or other ongoing commercial relationship; notifies the recipient of a change in their standing with respect to that ongoing commercial relationship; or provides regular, periodic account balance information to the recipient;
- provides information about an employment relationship or employee benefits; or
- delivers goods or services as part of a transaction that the recipient already has agreed to.
以及该警告内容：
Keep in mind that the law views these categories narrowly. That means you shouldn’t assume that any message you send to recipients who have an ongoing commercial relationship with you – including subscribers or recipients who participate in a membership program – are transactional or relationship messages.
这是大多数发件人在实践中犯的错误。拥有客户并不意味着你发给他们的邮件就是事务性邮件。向付费订阅者发送的产品资讯属于商业邮件，需要包含邮寄地址和退订方式。
发送平台中同样存在这种分类，正确设置它还有另一个原因：在 Bird 上，邮件类别决定退订是否生效。将营销邮件标记为事务性邮件不会使其免受法律约束，但会悄悄地使其绕过你自己的退订处理机制。
退订机制必须如何运作？
免费、简单，并在十个工作日内处理完毕。
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.
一句话中包含四项约束，每一项都排除了人们常见的做法：不能设置登录门槛、不能使用 "tell us why" 表单、不能设计多步骤向导、上月活动中的退订链接也不能失效。
退订之后还有进一步的限制。一旦有人选择了退出，"you can’t sell or transfer their email addresses, even in the form of a mailing list"，除非是交给帮助你合规的公司。
FTC 也允许使用偏好中心，但有一个条件：
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 marketing messages from you.
一个只提供 "fewer emails" 而没有完全退出选项的偏好中心不符合合规要求。
满足 CAN-SPAM 就够了吗？
仅当每位收件人都在美国境内，并且仅就法律问题而言。
有两个差距值得指出。在地域层面，CAN-SPAM 的选择退出模式属于例外：CASL 要求在发送第一封邮件前获得同意，欧洲规则同样如此。跨国的邮件列表受适用于每位收件人的最严格规则管辖，而非发件人所在地的规则。
另外，与法律无关的是，邮箱提供商也施加了 CAN-SPAM 未涉及的额外要求，包括一键退订和投诉率上限。法律合规与邮件送达是两个不同的问题。
简而言之
它不要求发送前获得同意。
与加拿大和欧洲的规则不同，CAN-SPAM 采用选择退出机制。它要求的是诚实、一个邮寄地址，以及一种有效的退订方式。
主要目的测试决定适用哪些规则。
邮件根据其主要用途来判定，FTC 的指南指出，商业性的主题行会使整封邮件被判定为商业邮件，无论正文内容是什么。
事务性邮件仅限五个固定类别。
与收件人存在持续关系并不能使邮件成为事务性邮件，FTC 表示这些类别应被严格解读。
退订处理期限为十个工作日，退订机制必须保持三十天有效。
你也不能收费、要求提供电子邮件地址以外的信息，或让用户在超过一个页面中操作。