Sendmail, 3rd Edition

Header Names

The name portion of the H configuration command must be one of the names shown in Table 25-1. Other names do not produce an error but might confuse other programs that need to process them. Names marked with an asterisk are defined by RFC2822.

Table 25-1. Header names

apparently-to	bcc*	cc*	comments*
content-length	content-transfer-encoding	content-type	date*
disposition	encrypted	errors-to	from*
full-name	in-reply-to*	keywords*	mail-from
message	message-id*	notification-to	posted-date
precedence	received*	references*	reply-to*
resent-bcc*	resent-cc*	resent-date*	resent-from*
resent-message-id*	resent-reply-to	resent-sender*	resent-to*
return-path*	return-receipt-to	sender*	subject*
text	to*	via	x400-received

These are discussed individually in Section 25.12 at the end of this chapter.

The RFC2822 standard allows a special form to be used for creating custom header names. All mail programs, including sendmail, are required to accept and pass through as is any header name that begins with the special characters x-. The following header definition, for example, can be used to introduce information that your site is running an experimental version of sendmail:

HX-Beware: This message used an experimental version of sendmail

The name part of header definitions is case-insensitive. That is, X-Beware, x-beware, and X-BEWARE are all the same. For example, when sendmail checks for the To: header internally, it will recognize it regardless ...