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Cytat
Do celu tam się wysiada. Lec Stanisław Jerzy (pierw. de Tusch-Letz, 1909-1966)
A bogowie grają w kości i nie pytają wcale czy chcesz przyłączyć się do gry (. . . ) Bogowie kpią sobie z twojego poukładanego życia (. . . ) nie przejmują się zbytnio ani naszymi planami na przyszłość ani oczekiwaniami. Gdzieś we wszechświecie rzucają kości i przypadkiem wypada twoja kolej. I odtąd zwyciężyć lub przegrać - to tylko kwestia szczęścia. Borys Pasternak
Idąc po kurzych jajach nie podskakuj. Przysłowie szkockie
I Herkules nie poradzi przeciwko wielu.
Dialog półinteligentów równa się monologowi ćwierćinteligenta. Stanisław Jerzy Lec (pierw. de Tusch - Letz, 1909-1966)
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.In many networks, it has become standardto prepend this data to the mail message, forming the so-called mail header.It is o setfrom the mail body by an empty line.11It is customary to append a signature or.si g to a mail message, usually containing information on theauthor, along with a joke or a motto.It is o set from the mail message by a line containing -- ". 13.1.What is a Mail Message? 214Most mail transport software in the un?x world uses a header format outlined in aRFC 822.Its original purpose was to specify a standard for use on the ARPANET, butsince it was designed to be independent from any environment, it has been easily adaptedto other networks, including many UUCP-based networks.RFC 822 however is only the greatest common denominator.More recent standards havebeen conceived to cope with growing needs as, for example, data encryption, internationalcharacter set support, and multi-media mail extensions MIME.In all these standards, the header consists of several lines, separated by newline charac-ters.A line is made up of a eld name, beginning in column one, and the eld itself, o setby a colon and white space.The format and semantics of each eld vary depending on theeld name.A header eld may be continued across a newline, if the next line begins witha TAB.Fields can appear in any order.A typical mail header may look like this:From brewhq.swb.de! ora.com! andyo Wed Apr 13 00: 17: 03 1994Return-Path: brewhq.swb.de! ora.com! andyoReceived: from brewhq.swb.de by monad.swb.de with uucpSmail3.1.28.1 6 id m0pqqlT-00023aB; Wed, 13 Apr 94 00: 17 MET DSTReceived: from ora.com ruby.ora.com by brewhq.swb.de with smtpSmail3.1.28.1 28.6 id m0pqoQr-0008qhC ; Tue, 12 Apr 94 21: 47 MESTReceived: by ruby.ora.com 8.6.8 8.6.4 id RAA26438; Tue, 12 Apr 94 15: 56 -0400Date: Tue, 12 Apr 1994 15: 56: 49 -0400Message-Id: 199404121956.PAA07787@rubyFrom: andyo@ora.com Andy OramTo: okir@monad.swb.deSubject: Re: Your RPC sectionUsually, all necessary header elds are generated by the mailer interface you use, likeelm, pine, mush, or mailx.Some however are optional, and may be added by the user.elm,for example, allows you to edit part of the message header.Others are added by the mailtransport software.A list of common header elds and their meaning are given below:From: This contains the sender's email address, and possibly the real name".Acomplete zoo of formats is used here.To: This is the recipient's email address.Subject: Describes the content of the mail in a few words.At least that's what itshould do.Date: The date the mail was sent. 13.1.What is a Mail Message? 215Reply-To: Speci es the address the sender wants the recipient's reply directed to.Thismay be useful if you have several accounts, but want to receive the bulk ofmail only on the one you use most frequently.This eld is optional.Organization:The organization that owns the machine from which the mail originates.If your machine is owned by you privately, either leave this out, or insertprivate" or some complete nonsense.This eld is optional.Message-ID: A string generated by mail transport on the originating system.It is uniqueto this message.Received: Every site that processes your mail including the machines of sender andrecipient inserts such a eld into the header, giving its site name, a messageid, time and date it received the message, which site it is from, and whichtransport software was used.This is so that you can trace which route themessage took, and can complain to the person responsible if something wentwrong.X-anything: No mail-related programs should complain about any header which startswith X-.It is used to implement additional features that have not yet madeit into an RFC, or never will.This is used by the Linux Activists mailinglist, for example, where the channel is selected by the X-Mn-Key: headereld.The one exception to this structure is the very rst line.It starts with the keywordFrom which is followed by a blank instead of a colon.To distinguish it from the ordinaryFrom: eld, it is frequently referred to as From.It contains the route the message hastaken in UUCP bang-path style explained below , time and date when it was received bythe last machine having processed it, and an optional part specifying which host it wasreceived from.Since this eld is regenerated by every system that processes the message,it is somtimes subsumed under the envelope data.The From eld is there for backward compatibilty with some older mailers, but is notused very much anymore, except by mail user interfaces that rely on it to mark the beginningof a message in the user's mailbox.To avoid potential trouble with lines in the messagebody that begin with From ", too, it has become standard procedure to escape any suchoccurence by preceding it with ". 13.2.How is Mail Delivered? 21613.2 How is Mail Delivered?Generally, you will compose mail using a mailer interface like mail or mailx; or more sophis-ticated ones like elm, mush, or pine.These programs are called mail user agents, or MUA'sfor short.If you send a mail message, the interface program will in most cases hand it toanother program for delivery.This is called the mail transport agent, or MTA.On somesystems, there are di erent mail transport agents for local and remote delivery; on others,there is only one.The command for remote delivery is usually called rmail, the other iscalled lmail if it exists.Local delivery of mail is, of course, more than just appending the incoming message tothe recipient's mailxbox.Usually, the local MTA will understand aliasing setting up localrecipient addresses pointing to other addresses , and forwarding redirecting a user's mail tosome other destination.Also, messages that cannot be delivered must usually be bounced,that is, returned to the sender along with some error message.For remote delivery, the transport software used depends on the nature of the link.Ifthe mail must be delivered over a network using TCP IP, SMTP is commonly used.SMTPstands for Simple Mail Transfer Protocol, and is de ned in RFC 788 and RFC 821.SMTPusually connects to the recipient's machine directly, negotiating the message transfer withthe remote side's SMTP daemon.In UUCP networks, mail will usually not be delivered directly, but rather be forwardedto the destination host by a number of intermediate systems.To send a message over aUUCP link, the sending MTA will usually execute rmail on the forwarding system usinguux, and feed it the message on standard input.Since this is done for each message separately, it may produce a considerable work loadon a major mail hub, as well as clutter the UUCP spool queues with hundreds of small lestaking up an unproportional amount of disk space.2 Some MTAs therefore allow you tocollect several messages for a remote system in a single batch le.The batch le containsthe SMTP commands that the local host would normally issue if a direct SMTP connectionwas used.This is called BSMTP, or batched SMTP.The batch is then fed to the rsmtp orbsmtp program on the remote system, which will process the input as if a normal SMTPconnection had occurred.2This is because disk space is usually allocated in blocks of 1024 Bytes.So even a message of at most400 Bytes will eat a full KB. 13.3.Email Addresses 21713.3 Email AddressesFor electronic mail, an address is made up of at least the name of a machine handlingthe person's mail, and a user identi cation recognized by this system.This may be therecipient's login name, but may also be anything else.Other mail addressing schemes, likeX.400, use a more general set of attributes" which are used to look up the recipient's hostin an X
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