.TH envelopes 5.SH "NAME"envelopes \- sender/recipient lists attached to messages.SH "INTRODUCTION"Electronic mail messages are delivered in.IR envelopes .An envelope lists a.I senderand one or more.IR recipients .Usually theseenvelope addresses are the sameas the addresses listed in the message header:.EX   (envelope) from djb to root.br   From: djb.br   To: root.EEIn more complicated situations, though,the envelope addresses may differ from the header addresses..SH "ENVELOPE EXAMPLES"When a message is delivered toseveral people at different locations,it is first photocopiedand placed into several envelopes:.EX   (envelope) from djb to root.br   From: djb                          Copy #1 of message.br   To: root, god@brl.mil.EE.EX   (envelope) from djb to god@brl.mil.br   From: djb                          Copy #2 of message.br   To: root, god@brl.mil.EEWhen a message is deliveredto several people at the same location,the sender doesn't have to photocopy it.He can instead stuff it intoone envelope with several addresses;the recipients will make the photocopy:.EX   (envelope) from djb to god@brl.mil, angel@brl.mil.br   From: djb.br   To: god@brl.mil, angel@brl.mil, joe, frde.EEBounced mail is sent back to the envelope sender address.The bounced mail doesn't list an envelope sender,so bounce loops are impossible:.EX   (envelope) from <> to djb.br   From: MAILER-DAEMON.br   To: djb.br   Subject: unknown user frde.EEThe recipient of a message may make another copyand forward it in a new envelope:.EX   (envelope) from djb to joe.br   From: djb                          Original message.br   To: joe.EE.EX   (envelope) from joe to fred.br   From: djb                          Forwarded message.br   To: joe.EEA mailing list works almost the same way:.EX   (envelope) from djb to sos-list.br   From: djb                          Original message.br   To: sos-list.EE.EX   (envelope) from sos-owner to god@brl.mil.br   From: djb                          Forwarded message.br   To: sos-list                       to recipient #1.EE.EX   (envelope) from sos-owner to frde.br   From: djb                          Forwarded message.br   To: sos-list                       to recipient #2.EENotice that the mailing list is set upto replace the envelope sender with something new,.BR sos-owner .So bounces will come back to.BR sos-owner :.EX   (envelope) from <> to sos-owner.br   From: MAILER-DAEMON.br   To: sos-owner.br   Subject: unknown user frde.EEIt's a good idea to set up an extra address,.BR sos-owner ,like this:the original envelope sender (\fBdjb\fP)has no way to fix bad.B sos-listaddresses,and of course bounces must not be sent to .B sos-listitself..SH "HOW ENVELOPE ADDRESSES ARE STORED"Envelope sender and envelope recipient addressesare transmitted and recorded in several ways.When a user injects mail through.BR qmail-inject ,he can supply a.B Return-Pathline or a.B \-foption for the envelope sender;by default the envelope sender is his login name.The envelope recipient addresses can be takenfrom the command line or from various header fields,depending on the options to.BR qmail-inject .Similar comments apply to.BR sendmail .When a message is transferred from one machine to another through SMTP,the envelope sender is given in a.B MAIL FROMcommand,the envelope recipients are given in .B RCPT TOcommands,and the message is supplied separately by a .B DATAcommand.When a message is delivered by.B qmailto a single local recipient,.B qmail-localrecords the recipient in.B Delivered-Toand the envelope sender in.BR Return-Path .It uses.B Delivered-Toto detect mail forwarding loops..B sendmailnormally records the envelope sender in.BR Return-Path .It does not record envelope recipient addresses,on the theory that they are redundant:you received the mail,so you must have been one of the envelope recipients.Note that,if the header doesn't have any recipient addresses,.B sendmailwill move envelope recipient addresses back into the header.This situation occurs if all addresses were originally listed as.BR Bcc ,since.B Bccis automatically removed.When.B sendmailsees this, it creates a new.B Apparently-Toheader field with the envelope recipient addresses.This has the strange effect that each blind-carbon-copy recipient will seea list of all recipients on the same machine.When a message is stored in.B mboxformat,the envelope sender is recorded at the top of the messageas a UUCP-style.B From(no colon) line.Note that this line is less reliable than the.B Return-Pathline added by.B qmail-localor.B sendmail\fP..SH "SEE ALSO"qmail-header(5),qmail-local(8),qmail-inject(8)