Posting style

When a message is replied to in e-mail, Internet forums, or Usenet, the original can often be included, or "quoted", in a variety of different posting styles.

The main options are interleaved posting (also called inline replying, in which the different parts of the reply follow the relevant parts of the original post), bottom-posting (in which the reply follows the quote) or top-posting (in which the reply precedes the quoted original message). For each of those options, there is also the issue of whether trimming of the original text is allowed, required or preferred.

For a long time the traditional style was to post the answer below as much of the quoted original as was necessary to understand the reply (bottom or inline). Many years later, when email became widespread in business communication, it became a widespread policy to reply above the entire original and leave it (supposedly untouched) below the reply.

While each online community differs on which styles are appropriate or acceptable, within some communities the use of the "wrong" method risks being seen as a breach of netiquette, and can provoke vehement response from community regulars.

In an e-mail reply, it is sometimes appropriate to include a full or partial copy of the original message that is being replied to. As opposed to in-person conversations and Internet chats, email responses may be received long after the original message was sent, so the original sender may have forgotten, misplaced or deleted the original. Many email reading programs (mail user agents) encourage this behavior by automatically including a copy of the original message in the reply editing window.

Quoted text from previous messages is usually distinguished in some way from the new (reply) text. At a minimum, the two parts are given different indentation. In the example below, the first line is the original message, the second line is the reply:

Alternatively, special delimiter lines may be used:

For extra clarity, blank lines may also be inserted between the two parts. When using an email medium that supports text markup (such as HTML or RTF), the previous text may be indicated by a distinctive font and/or color:

A common convention in plain-text email is to prefix each line of the quoted text with a distinctive character or string. Today (and for many years previously), the greater-than sign (">", the prefix) is almost universally used; but other characters such as the ASCII vertical bar character ("|") have been used as well, sometimes with one or more spaces inserted before or after the quoted text marker.

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Wikipedia