email.message.Message ：表示 Email 消息使用 compat32 API ¶

The Message 类非常类似于 EmailMessage 类，没有由该类添加的方法，且某些其它方法的默认行为稍有不同。这里还文档化了一些方法，虽然支持是通过 EmailMessage 类，不推荐除非正处理传统代码。

这 2 个类的哲学和结构在其它方面是相同的。

此文档描述的行为在默认 (对于 Message ) 策略 Compat32 。若打算使用其它策略，应使用 EmailMessage 类代替。

Email 包含 headers 和 payload 。Header 头必须是 RFC 5322 样式的名称和值，其中字段名称和值由冒号分隔。冒号不属于字段名称或字段值。负载可以是简单文本消息、二进制对象、或结构化的子消息序列 (每个子消息有自己的一组头和负载)。后一种类型的负载由拥有 MIME (多用途 Internet 邮件扩展) 类型的消息指示，譬如 multipart/* or message/rfc822 .

概念模型的提供通过 Message object is that of an ordered dictionary of headers with additional methods for accessing both specialized information from the headers, for accessing the payload, for generating a serialized version of the message, and for recursively walking over the object tree. Note that duplicate headers are supported but special methods must be used to access them.

The Message pseudo-dictionary is indexed by the header names, which must be ASCII values. The values of the dictionary are strings that are supposed to contain only ASCII characters; there is some special handling for non-ASCII input, but it doesn’t always produce the correct results. Headers are stored and returned in case-preserving form, but field names are matched case-insensitively. There may also be a single envelope header, also known as the Unix-From header or the From_ 头。 payload is either a string or bytes, in the case of simple message objects, or a list of Message objects, for MIME container documents (e.g. multipart/* and message/rfc822 ).

这里是方法对于 Message 类：

class email.message. 消息 ( policy = compat32 ) ¶

若 policy 有指定 (它必须是实例化的 policy 类) 使用它指定的规则来更新和序列化消息表示。若 policy 未设置，使用 compat32 策略，保持向后兼容 Python 3.2 版 email 包。更多信息见 policy 文档编制。

3.3 版改变： The policy 关键词自变量被添加。