从信封 To 和 From 地址构建 Received 标题行

关键字：receivedfor、noreceivedfor、receivedfrom、noreceivedfrom

receivedfor 关键字指示 MTA，如果邮件只发给一个信封收件人，则将该信封 To: 地址包含在其构建的 Received: 标题行中。关键字 receivedfor 是默认设置。noreceivedfor 关键字指示 MTA 构建 Received: 标题行，但不包含任何信封地址信息。

receivedfrom 关键字指示 MTA，如果 MTA 由于某些种类的邮件列表扩展等原因而更改了信封 From: 地址，则在为外来邮件构建 Received: 标题行时包含原来的信封 From: 地址。receivedfrom 是默认设置。noreceivedfor 关键字指示 MTA 构建 Received: 标题行，但不包含原来的信封 From: 地址。