.TH qmail-header 5.SH NAMEqmail-header \- format of a mail message.SH OVERVIEWAt the top of every mail message is ahighly structured.BR header .Many programs expect the header to carry certain information,as described below.The main function of.B qmail-injectis to make sure that each outgoing message has an appropriate header.For more detailed information, see.BR http://pobox.com/~djb/proto/immhf.html ..SH "MESSAGE STRUCTURE"A message contains a series of.I header fields\fR,a blank line,and a.IR body :.EX     Received: (qmail-queue invoked by uid 666);.br	     30 Jul 1996 11:54:54 -0000.br     From: djb@silverton.berkeley.edu (D. J. Bernstein).br     To: fred@silverton.berkeley.edu.br     Date: 30 Jul 1996 11:54:54 -0000.br     Subject: Go, Bears!.br.br     I've got money on this one.  How about you?.br.br     ---Dan   (this is the third line of the body).EEEach header field has a.IR name ,a colon,some.IR contents ,and a newline:.EX     Subject: Go, Bears!.EEThe field contents may be folded across several lines.Each line past the first must begin with a space or tab:.EX     Received: (qmail-queue invoked by uid 666);.br	     30 Jul 1996 11:54:54 -0000.EEThe field name must not contain spaces, tabs, or colons.Also, an empty field name is illegal..B qmail-injectdoes not allow field names with unprintable characters.Case is irrelevant in field names:.B subjectand.B SUBJECTand.B SuBjEcThave the same meaning..SH "ADDRESS LISTS"Certain fields, such as.BR To ,contain.I address lists\fR.An address list contains some number of.I addressesor.I address groups\fR,separated by commas:.EX     a@b, c@d (Somebody), A Person <e@f>,.br        random group: g@h, i@j;, k@l.EEAn.I address grouphas some text, a colon, a list of addresses,and a semicolon:.EX        random group: g@h, i@j;.EEAn address can appear in several forms.The most common form is.IR box@host .Every address must include a host name.If.B qmail-injectsees a lone box nameit adds the.I default host name\fR.All host names should be fully qualified..B qmail-injectappends the.I default domain nameto any name without dots:.EX     djb@silverton  ->  djb@silverton.berkeley.edu.EEIt appends the.I plus domain nameto any namethat ends with a plus sign:.EX     eric@mammoth.cs+  ->  eric@mammoth.cs.berkeley.edu.EEA host name may be a dotted-decimal address:.EX     djb@[128.32.183.163].EERFC 822 allows mailbox names inside angle bracketsto include.I source routes\fR,but.B qmail-injectstrips all source routes out of addresses..SH "SENDER ADDRESSES".B qmail-injectlooks for sender address lists in the following fields:.BR Sender ,.BR From ,.BR Reply-To ,.BR Return-Path ,.BR Return-Receipt-To ,.BR Errors-To ,.BR Resent-Sender ,.BR Resent-From ,.BR Resent-Reply-To .If there is no.B Fromfield,.B qmail-injectadds a new.B Fromfield with the name of the user invoking.B qmail-inject.RFC 822 requires that certain sender fields containonly a single address, but.B qmail-injectdoes not enforce this restriction..SH "RECIPIENT ADDRESSES".B qmail-injectlooks for recipient address lists in the following fields:.BR To ,.BR Cc ,.BR Bcc ,.BR Apparently-To ,.BR Resent-To ,.BR Resent-Cc ,.BR Resent-Bcc .Every message must contain at least one.B Toor.B Ccor.BR Bcc ..B qmail-injectdeletes any.B Bccfield.If there is no.B Toor.B Ccfield,.B qmail-injectadds a line.EX     Cc: recipient list not shown: ;.EEThis complies with RFC 822;it also works around some strange.B sendmailbehavior, in case the message is passed through.B sendmailon another machine..SH STAMPSEvery message must contain a.B Datefield, with the date in a strict format defined by RFC 822.If necessary.B qmail-injectcreates a new.B Datefield with the current date (in GMT).Every message should contain a.B Message-Idfield.The field contents are a unique worldwide identifier for this message.If necessary.B qmail-injectcreates a new.B Message-Idfield.Another important field is.BR Received .Every time the message is sent from one system to another,a new.B Receivedfield is added to the top of the message..B qmail-injectdoes not create any.B Receivedfields..SH "RESENT MESSAGES"A message is.I resentif it contains any of the following fields:.BR Resent-Sender ,.BR Resent-From ,.BR Resent-Reply-To ,.BR Resent-To ,.BR Resent-Cc ,.BR Resent-Bcc ,.BR Resent-Date ,.BR Resent-Message-ID .If a message is resent,.B qmail-injectchanges its behavior as follows.It deletes any.B Resent-Bccfield (as well as any.B Bccfield);if there are no.B Resent-Toor.B Resent-Ccfields,.B qmail-injectadds an appropriate.B Resent-Ccline.It does.I notadd a.B Ccline,even if neither.B Tonor.B Ccis present.If there is no.B Resent-Fromfield,.B qmail-injectadds a new.B Resent-Fromfield.It does.I notadd a new.B Fromfield..B qmail-injectadds.B Resent-Dateif one is not already present;same for.BR Resent-Message-Id .It does.I notadd new.B Dateor.B Message-Idfields..SH "OTHER FEATURES"Addresses are separated by commas, not spaces.When.B qmail-injectsees an illegal space,it inserts a comma:.EX     djb fred  ->  djb, fred.EE.B qmail-injectremoves all.B Return-Pathheader fields..B qmail-injectalso removes any.B Content-Lengthfields..SH "SEE ALSO"addresses(5),envelopes(5),qmail-inject(8)