MH processes messages in a particular format. Although neither Bell nor Berkeley mailers produce message files in the format that MH prefers, MH can read message files in that format.
Each user has a maildrop that initially receives all messages processed by the post command (see post(8)).
The inc command reads from the maildrop and incorporates the new messages found there into the user's own +inbox folder. The maildrop consists of one or more messages.
Messages are expected to consist of lines of text. Graphics and binary data are not handled. No data compression is accepted. All text is in ASCII 7-bit data.
The general memo framework of RFC 822 is used. A message consists of a block of information in a rigid format, followed by general text with no specified format. The rigidly-formatted first part of a message is called the message header; the free-format portion is called the body. The header must always exist, but the body is optional. These parts are separated by a blank line or by a line of dashes. The following example shows the standard default MH mail header:
To: cc: Subject: --------
The header is composed of one or more header items. Each header item can be viewed as a single logical line of ASCII characters. If the text of a header item extends across several real lines, the continuation lines are indicated by leading spaces or tabs.
Each header item is called a component and is composed of a keyword or name, along with associated text. The keyword begins at the left margin, and is terminated by a colon (:). It cannot contain spaces or tabs, and cannot exceed 63 characters, as specified by RFC 822.
The text for most formatted components, such as Date: and Message-Id:, is produced automatically. The user enters address fields such as To: and cc:, and the Subject: field. Internet addresses are assigned mailbox names and host computer specifications. The general format is local@domain, for example, MH@UCI or MH@UCI-ICSA.ARPA. A comma (,) separates multiple addresses. A missing host/domain is assumed to be the local host/domain.
A blank line (or a line of dashes) signals that all following text up to the end of the file is the body of the message. No formatting is expected or enforced within the body.
The following is a list of header components that are considered meaningful to MH programs: Added by post, contains the date and time of the message's entry into the transport system. Added by post, contains the address of the author or authors (there may be more than one if a Sender: field is present). Replies are typically directed to addresses in the Reply-To: or From: field. The former has precedence, if present. Added by post in the event that the message already has a From: line. This line contains the address of the actual sender. Replies are never sent to addresses in the Sender: field. Contains addresses of primary recipients. Contains addresses of secondary recipients. Contains the addresses of recipients who receive blind carbon copies of the message. The Bcc: line does not appear on the message as sent, so these recipients are not listed. Recipients in the Bcc: field receive a copy of the message with a minimal header. MH uses an encapsulation method for blind copies; see send(1). Causes post to copy the message into the specified folder for the sender, if the message was successfully given to the transport system. A unique message identifier added by post, if the -msgid flag is set. Sender's commentary. It is displayed by scan. A commentary line added by repl when replying to a message. Added by post when a message is redistributed. Added by post when a message is redistributed. New recipients for a message resent by dist. New secondary recipients for a message resent by dist. New blind carbon copy recipients for a message resent by dist. Places a copy of a message resent by dist into the sender's folder. A unique identifier of a message resent by dist. This is appended by post if the -msgid flag is set. Annotation added by dist when the -annotate flag is specified. Annotation added by forw when the -annotate flag is specified. Annotation added by repl when the -annotate flag is specified. Specifies the MIME version number. This header entry is used or added by MH software only when codeset conversion of mail messages is enabled and requested. For more information on codeset conversion, see the section on internationalization features in mh(1). Specifies the content type, which is always TEXT/PLAIN, plus a charset value that names a coded character set (codeset). This header entry is used or added by MH software only when codeset conversion of mail messages is enabled and requested. For more information on codeset conversion, see the section on internationalization features in mh(1).
Standard location of mail drop
Standard for the Format of ARPA Internet Text Messages (RFC 822) delim off