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SMTP
Posted Date: 17 May 2008 Resource Type: Articles/Knowledge Sharing Category: Computer & Technology
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Posted By: Shanthi M Member Level: Diamond
Rating:  Points: 1
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SMTP(pronounced as separate letters) Short for Simple Mail Transfer Protocol, a protocol for sending e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP. In addition, SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP or IMAP server and the SMTP server when you configure your e-mail application.
SMTP Protocol Overview
Simple Mail Transfer Protocol (SMTP), documented in RFC 821, is Internet's standard host-to-host mail transport protocol and traditionally operates over TCP, port 25. In other words, a UNIX user can type telnet hostname 25 and connect with an SMTP server, if one is present.
SMTP uses a style of asymmetric request-response protocol popular in the early 1980s, and still seen occasionally, most often in mail protocols. The protocol is designed to be equally useful to either a computer or a human, though not too forgiving of the human. From the server's viewpoint, a clear set of commands is provided and well-documented in the RFC. For the human, all the commands are clearly terminated by newlines and a HELP command lists all of them. From the sender's viewpoint, the command replies always take the form of text lines, each starting with a three-digit code identifying the result of the operation, a continuation character to indicate another lines following, and then arbitrary text information designed to be informative to a human.
If mail delivery fails, sendmail (the most important SMTP implementation) will queue mail messages and retry delivery later. However, a backoff algorithm is used, and no mechanism exists to poll all Internet hosts for mail, nor does SMTP provide any mailbox facility, or any special features beyond mail transport. For these reasons, SMTP isn't a good choice for hosts situated behind highly unpredictable lines (like modems). A better-connected host can be designated as a DNS mail exchanger, then arrange for a relay scheme. Currently, there two main configurations that can be used. One is to configure POP mailboxes and a POP server on the exchange host, and let all users use POP-enabled mail clients. The other possibility is to arrange for a periodic SMTP mail transfer from the exchange host to another, local SMTP exchange host which has been queuing all the outbound mail. Of course, since this solution does not allow full-time Internet access, it is not too preferred.
RFC 1869 defined the capability for SMTP service extensions, creating Extended SMTP, or ESMTP. ESMTP is by definition extensible, allowing new service extensions to be defined and registered with IANA. Probably the most important extension currently available is Delivery Status Notification (DSN), defined in RFC 1891.
What is SMTP?
The network protocol used to send email across the Internet
Simple Mail Transport Protocol (SMTP) is the network protocol used to send email across the Internet. When you send email, its first stop is a server running SMTP. The primary UW SMTP (mail-sending) server is smtp.washington.edu (The older UW SMTP server, mailhost.washington.edu, is scheduled to be removed from service on August 14, 2006.)
When do you need to know about SMTP?
When configuring your desktop email software
You DO NOT need to know about SMTP if you are using email software running on a computer other than your own (e.g, Pine on Dante or Homer; WebPine on MyUW). You can stop reading here.
You DO need to know the UW SMTP server name if you are running email software (e.g., Outlook Express, PC-Pine) on your own desktop computer, and want to configure your software to work with UW email servers. When you edit the configuration file and get to the "Outgoing Mail Server" (SMTP) question, you enter smtp.washington.edu, if you are using a UW-provided Internet connection (i.e., campus ethernet or UW dial-up modem).
If you're NOT using a UW-provided Internet connection, you need to contact your Internet Service Provider (ISP) and ask for the SMTP server name to use for "Outgoing Mail Server."
When do you need SMTP authentication and encryption?
When use of a non-UW-provided Internet connection restricts your use of UW email or when you want to send encrypted email
Things get complicated when you want to use UW email with your desktop email client AND a non-UW-provided Internet connection (e.g., dialup, cable, DSL).
Problem
Email ORIGINATING OUTSIDE the UW (i.e., from a non-UW network) and DESTINED for an address OUTSIDE the UW is not accepted by smtp.washington.edu unless the connection is authenticated and encrypted. This policy prevents the UW SMTP server from becoming a "spam relay," forwarding on junk email coming and going across the Internet.
Solution
Setting the SMTP authentication and encryption option when configuring your desktop software solves this problem, as well as giving added security to your email.
Note: If you are using Norton Antivirus software, be sure the "Scan Outgoing Email" feature is turned off before connecting to the UW SMTP server.
"Scan Outgoing Email" feature is turned off before connecting to the UW SMTP server.
Examples
You want to use the SMTP authenticiation and encryption option if:
• Your ISP (dialup, cable, DSL) has a policy that restricts use of their SMTP server if the "reply to" address is not within their domain. (i.e, set up like the UW SMTP to help prevent email spam)
This creates a problem when you want your reply address to be your_uwnetid@u.washington.edu
[Note: In rare cases, an ISP may only permit access to port 25 (the usual SMTP port) for use of its own SMTP server, AND may restrict use of its SMTP server. If this is the case, use the UW SMTP server (smtp.washington.edu) with authentication and encryption set, and specify the port number 587.]
• You connect to the campus network using the same computer (e.g., a laptop) for both UW-provided Internet connections and a third party ISP.
This creates a problem since your SMTP setting is different with each ISP. The SMTP server is generally specified as part of the email software configuration and not easily changed "on the fly." You might connect using the UW-provided connection (campus ethernet or UW dial-up modem) and other times using a third party (dial-up or cablemodem, DSL).
• You want to encrypt your email communications. (Your local departmental policy may require it.)
Note of caution: Encrypting the communication between your computer and the FIRST SMTP server does NOT guarantee the message will be encrypted ALL the way to its destination.
How do you set up the SMTP authentication and encryption option?
By correctly configuring desktop email software that is compatible with the UW SMTP server
In general, you configure your desktop email software to use SMTP authentication and encryption by using "TLS for SSL" (i.e., "STARTTLS"), setting it to either "required" or "if available," and/or "permit authorization." Specific configuration directions are available on the individual software Web pages.
Compatible Desktop Email Software
The desktop email software below is known to be compatible with the SMTP authentication and encryption software (STARTTLS) implemented on smtp.washington.edu Click the software name for configuration details.
• Mozilla Thunderbird instructions for Windows
• Mozilla Thunderbird instructions for Macintosh (OS X only)
• Mozilla Mail instructions for Windows
• Mozilla Mail instructions for Macintosh
• PC-Pine instructions
• Mac OS X Mail instructions
• Outlook Express instructions for Windows
• Outlook Express for Macintosh cannot be configured to use authenticated SMTP
Non-compatible Desktop Email Software
The following email software is known to have settings available that APPEAR to provide STARTTLS (the authentication and encryption software), but they are NOT compatible with the smtp.washington.edu server:
Apple Macintosh:
• Outlook Express (tested through version 5.06)
• Entourage (tested through version 10.1.4)
• Eudora (tested through version 5.1) (C&C does not support Eudora)
Changes to Outgoing E-mail Server (Read me first)
The outgoing mail (SMTP) server for University of Calgary users is changing from mailhost.ucalgary.ca to smtp.ucalgary.ca. Off-campus users, reznet, dialup and AirUC users are required to make the transition by March 31, 2004. Some connections have already been closed. We will be scanning usage logs and periodically sending reminders to these users.
Using this server requires authentication with Information Technologies username and password --same one as you use to read your IT e-mail. Typically you will be prompted for your password when you send the first message of your session. Below are instructions for making the change to your E-mail preferences.
Authentication will allow IT to then block spammers from relaying spam via our servers. U of C IT users will be able to avoid having e-mail rejected when travelling and using other ISPs off-campus. See note about travelling.
This server supports SSL/TLS encryption to make your e-mail more secure in transit. Some mail programs (Eudora, Entourage) do not work with current server SSL. Some firewalls, routers, and antivirus software will not work with SSL. Norton Antivirus users should check here. Selecting SSL/TLS is optional but recommended if available and working.
UC IT suggests changing your Incoming E-mail server from x.imap.ucalgary.ca to imap.ucalgary.ca and again to select secure socket layer SSL to encrypt and also to avoid certificate popups.
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Responses
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| Author: Prasad 18 May 2008 | Member Level: Gold Points : 2 | Very good Shanthi. Where are you getting these type of useful information?
| | Author: Vidya 20 May 2008 | Member Level: Diamond Points : 2 | useful information
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