An Overview of Protocols and Function

Transcription

1 An Overview of Protocols and Function

2 A Brief History of or (both spellings are acceptable) is short for electronic mail predates the inception of the Internet, and was in fact a crucial tool in creating the Internet. In the 60s it was a way to facilitate communication for time-sharing computers Ray Tomlinson initiated the use of symbol to separate the name of the user form their machine in 1971.

3 Plain Text and HTML Both plain text and HTML are used to convey Text is certain to be read by all users without problems, there is a perception that HTMLbased has a higher aesthetic value.

4 Advantages and Disadvantages Advantages of HTML are that you are able to: Include links and images Word wrap naturally on any display use emphasis such as underlines and italics change font styles Some disadvantages include: Increased size of the message privacy concerns about web bugs messages can be used for phishing attacks and to spread malicious software

5 SMTP Simple Mail Transfer Protocol: Conceived and developed by ARPA in the 1960s Used to forward messages from one host to another Very simple protocol that runs directly on the TCP/IP (Transmission control protocol/internet protocol)

6 POP3 Post Office Protocol 3 The third iteration of POP (4 th in the works, starting to roll out) Like STMP runs on the TCP/IP Used by the user to retrieve a message from the machine to which the SMTP has forwarded a message Works hand-in-hand with SMTP

7 What makes up a Valid Address (Review) An address can be broken up into four parts: local-part@subdomain.domain.tld Cannot be an empty or zero length string Domain portion cannot contain any of the following characters: ~ ' ^ ` " * + = \ ] [ ( ) { } $ &! # % / :, ; (spaces) NOTE: the local part (i.e. the part before symbol) can Valid address cannot have a '.' in last or second last position There must be one, and only symbol in the address There cannot be a. Immediately following symbol There must be at least one. after symbol (just not immediately after it) Two periods (. ) cannot be side-by-side in the address

8 PHP Validation (Review) The majority of scripting or programming languages require that you code a validator Something that accepts a String argument and return a boolean depending on whether the string passed conform to the valid rules PHP, as its sole purpose is for use on the web, provides a predefined funtion: filter_var ()

9 filter_var() (REVIEW) The filter_var() function can filter out several things For the purposes of this course, it shall be used to filter invalid address strings The syntax is: filter_var($a_string_arg, FILTER_VALIDATE_ ); This will either return a boolean false (if the string argument is an invalida ), or the string argument itself (if the string is a valid address) NOTE: the FILTER_VALIDATE_ is a predefined PHP constant, that tells the function what it is filtering See:

10 <?php?> Simple filter_var() Example //comes from if(!filter_var( FILTER_VALIDATE_ )) { echo(" is not valid"); } else { echo(" is valid"); }

11 <?php?> Realistic filter_var() Example $error = ; //an error message variable, initially empty //embed in a page with an input box named _address and //have the form submit here in POST mode $ = trim($_post[ _address ]); //trim whitespace if(strlen($ ) == 0){ //use strlen() to det. whether var empty or not $error.= You must enter an address ; }else if(!filter_var($ , FILTER_VALIDATE_ )){ } //note the! not symbol, if valid no problem $error.= $ . is not a valid address ; //note: give the invalid address so user knows $ = ; //empty out the variable so it is not sticky

12 PHP mail() Function bool mail ( string $to, string $subject, string $message [, string $additional_headers [, string $additional_parameters ]] ) N.B. Subject should not conatin any newline characters In the message each line should be separated with a LF (\n). Lines should not be larger than 70 characters. The additional headers (which are optional) is a string to be inserted at the end of the header Returns TRUE if the mail was successfully accepted for delivery, FALSE otherwise. For delivery means the local SMTP will attempt to send, it has nothing to do with whether it was actually delivered or not.

13 PHP mail() Example <?php //first_mail.php $mail_to $mail_subject = "Hi there!" ; $mail_body = "We'll have a meeting next Wednesday.\n"; $mail_body.= "7 P.M. in Judy's Office.\n"; $mail_body.= "Oh, BYOB!\n"; if(mail($mail_to, $mail_subject, $mail_body)) echo \"$mail_subject\" to $mail_to was accepted for sending."; else echo " \"$mail_subject\" to $mail_to was not accepted for sending."?>

14 A More Realistic Example <?php $to = 'nobody@example.com'; $subject = The Subject'; $message = 'hello'; $headers = 'From: webmaster@example.com'. "\r\n". 'Cc: someoneelse@a.com\r\n Bcc: hidden@gmail.com. 'Reply-To: webmaster@example.com'. "\r\n". 'X-Mailer: PHP/'. phpversion(); mail($to, $subject, $message, $headers);?> The \r are what the system needs to delimit your header N.B. When sending mail, the mail must contain a From header. This can be set with the additional_headers parameter, or a default can be set in php.ini

15 PHP Bulk Mail Example <?php //mass_mail.php $team_mates = "./teammates_ .txt"; $ s = file($team_mates); for($i=0; $i < count($ s); $i++) $ s[$i] = trim($ s[$i]); $recipients = implode( ;", $ s); $mail_subject = "Hi there!"; $mail_body = "We'll have a meeting next Wednesday.\n"; $mail_body.= "7 P.M. in Judy's Office.\n"; $mail_body.= "Oh, BYOB!\n"; mail($recipients, $mail_subject, $mail_body); echo "Successfully sent the \"$mail_subject\" to $recipients.";?>

16 Spam also known as "bulk " or "junk ," involves nearly identical messages sent to numerous recipients by . A common synonym for spam is unsolicited bulk e- mail (UBE). Sending spam violates the Acceptable Use Policy (AUP) of almost all Internet Service Providers. Providers vary in their willingness or ability to enforce their AUP. Some actively enforce their terms and terminate spammers' accounts without warning. Some ISPs lack adequate personnel or technical skills for enforcement, while others may be reluctant to enforce restrictive terms against profitable customers.

17 Spam Stats An spam is sent to 600 addresses (all of the ARPANet users at the time) First large-scale spam sent to 6000 newsgroups, reaching millions of people (June) 30 billion per day (June) 55 billion per day (December) 85 billion per day (February) 90 billion per day billion per day estimates the amount of spam was between 88 92% of messages sent in the first half of 2010 A 2004 survey estimated that lost productivity costs Internet users in the United States $21.58 billion annually, while another reported the cost at $17 billion, up from $11 billion in 2003 Data from: