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Email forwarding generically refers to the operation of re-sending an email message delivered to one email address on to a possibly different email address. The term ''forwarding'' has no specific technical meaning.〔In section 3.9.2 ''List'' of RFC 5321, the term ''forwarding'' is used ambiguously. It notes that "''the key difference between handling aliases (Section 3.9.1) and forwarding (this subsection) is the change to the (header )''." That wording, new w.r.t. RFC 2821, could be interpreted as the definition of ''forwarding'', if the same term weren't used at the beginning of the same subsection with the opposite meaning. As a contributor to Users and administrators of email systems use the same term when speaking of both server-based and client-based forwarding. Email forwarding can also redirect mail going to one address and send it to one or several other addresses. ''Vice versa'', email items going to several different addresses can converge via forwarding to end up in a single address in-box. == Server-based forwarding == The domain name (the part appearing to the right of ''@'' in an email address) defines the target server(s)〔 The primary MX record of the relevant domain usually publishes the name of the mail server. Otherwise the domain name must have an IP address. 〕 for the corresponding class of addresses. A domain may also define backup servers; they have no mailboxes and ''forward'' messages without changing any part of their envelopes.〔The ''envelope'' of a message is the data transmitted in an SMTP transaction before transmitting the ''content'' of the message. The envelope is lost when the message is delivered, although some of its fields may be saved by the receiving server in the message's headers. In particular, the envelope holds the ''Return-Path'' (a.k.a. bounce address, ''MAIL FROM'' argument, ''mailfrom'', or ''mfrom'') and one or more ''recipients'' (including ''Bcc'' Email administrators sometimes use the term redirection as a synonym for server-based email-forwarding to different recipients. Protocol engineers sometimes use the term Mediator to refer to a forwarding server. Because of spam, it is becoming increasingly difficult to reliably forward mail across different domains, and some recommend avoiding it if at all possible. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Email forwarding generically refers to the operation of re-sending an email message delivered to one email address on to a possibly different email address. The term ''forwarding'' has no specific technical meaning.In section 3.9.2 ''List'' of RFC 5321, the term ''forwarding'' is used ambiguously. It notes that "''the key difference between handling aliases (Section 3.9.1) and forwarding (this subsection) is the change to the (header )''." That wording, new w.r.t. RFC 2821, could be interpreted as the definition of ''forwarding'', if the same term weren't used at the beginning of the same subsection with the opposite meaning. As a contributor to RFC 5321 agreed, .Users and administrators of email systems use the same term when speaking of both server-based and client-based forwarding.Email forwarding can also redirect mail going to one address and send it to one or several other addresses. ''Vice versa'', email items going to several different addresses can converge via forwarding to end up in a single address in-box.== Server-based forwarding ==Sender Policy Framework」の詳細全文を読む スポンサード リンク
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