Header-name: OPTION=VALUE, OPTION=VALUE, OPTION=VALUE, ...

ADD (Quoted String)

Creates a new header line of the given type. The new header line contains the specified string. The header line created by ADD appears after any existing header lines of the same type. The ADD option cannot be used in conjunction with the Defaults header line type; it is ignored if it is specified as part of an Other: option list.

FILL

(Quoted String) 

Creates a new header line of the given type only if there are no existing header lines of the same type. The new header line contains the specified string. The FILL option cannot be used in conjunction with the header line type; it is ignored if it is specified as part of an Other option list.

GROUP

(Integer 0 or 1) 

Controls grouping of header lines of the same type at a particular precedence level. A GROUP value of 0 is the default, and indicates that all header lines of a particular type should appear together. A value of 1 indicates that only one header line of the respective type should be output and the scan over all header lines at the associated level should resume, leaving any header lines of the same type unprocessed. Once the scan is complete it is then repeated in order to pick up any remaining header lines. This header option is primarily intended to accommodate Privacy Enhanced Mail (PEM) header processing.

LINELENGTH (Integer)

Controls the length at which to fold headers. See the headerlinelength channel keyword.

MAXCHARS (Integer)

Controls the maximum number of characters that can appear in a single header line of the specified type. Any header line exceeding that length is truncated to a length of MAXCHARS. This option pays no attention to the syntax of the header line and should never be applied to header lines containing addresses and other sorts of structured information. The length of structured header lines should instead be controlled with the maxheaderchars and maxheaderaddrs channel keywords.

MAXIMUM (Integer)

Controls the maximum number of header lines of this type that may appear. This has no effect on the number of lines; after wrapping, each individual header line can consume. A value of -1 is interpreted as a request to suppress this header line type completely.

MAXLINES (Integer)

Controls the maximum number of lines all header lines of a given type may occupy. It complements the MAXIMUM option in that it pays no attention to how many header lines are involved, only to how many lines of text they collectively occupy. As with the MAXIMUM option, headers are trimmed from the bottom to meet the specified requirement.

PRECEDENCE (Integer)

Controls the order in which header lines are output. All header lines have a default precedence of zero. The smaller the value, the higher the precedence. Positive PRECEDENCE values push header lines toward the bottom of the header while negative values push them toward the top. Equal precedence ties are broken using the MTA's internal rules for header line output ordering.

RELABEL (header name)

Changes a header line to another header line; that is, the name of the header is changed, but the value remains the same. For instance, 

X-MSMail-Priority: RELABEL="Priority"

X-Priority: RELABEL="Importance"