V8 sendmail offers a number of m4 macros for use in your mc configuration file that deal directly with headers. They are shown in Table 25-4.

Table 25-4. Header-related mc macros
Macro	§	Sets What
`confFROM_HEADER`	From:	Define the format for the `From:` header
`confRECEIVED_HEADER`	Received:	Define the format for the `Received:` header
`confOLD_STYLE_HEADERS`	OldStyleHeaders	Declare the `OldStyleHeaders` option
`confMAX_HEADERS_LENGTH`	MaxHeadersLength	Declare the `MaxHeadersLength` option
`confMAX_MIME_HEADER_LENGTH`	MaxMimeHeaderLength	Declare the `MaxMimeHeaderLength` option
`confSINGLE_LINE_FROM_HEADER`	SingleLineFromHeader	Declare the `SingleLineFromHeader` option
`confUSE_ERRORS_TO`	UseErrorsTo	Declare the `UseErrorsTo` option, which affects the `Errors-To:` header
`confNO_RCPT_ACTION`	NoRecipientAction	Declare the `NoRecipientAction` option, which affects the `To:`, `Cc:`, and `Bcc:` headers
`confRRT_IMPLIES_DSN`	RrtImpliesDsn	Declare the `RrtImpliesDsn` option, which affects the `Return-Receipt-To:` header