what is email adddress? what is user @ domain name? what is the format of a mail? - Cyber security & Technology

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Saturday, July 21, 2018

what is email adddress? what is user @ domain name? what is the format of a mail?





E-MAIL ADDRESS


·        Every e-mail is identified by a unique e-mail address.

·        It consists of a characters string identifying a person and the computer to . which a mail is to be delivered.

·        The format for an e-mail address is: 

User @ domain name


·        The user part identifies the mail box of the user in the domain indicated in the domain part of the address. The user part is unique within the domain.

·        Domain name part identifies some organization or a host machine that provides mailbox service and it is unique globally. The host machine represented in an e-mail address is also known as mail server or exchange. The domain name assigned to each mail exchange comes from the DNS database or is a logical name (for example, the name of the organization).

·        Some of the important factors that must be kept is mind with respect to e- mail address are:

1.       It is possible to have same usernames in different domains. For example : . charanjeetss@gmail.com and charanjeeetss@yahoo.com.

2.      E-mail addresses are not case sensitive i.e. both uppercase and lowercase characters are same.

3.      It is not possible to use space in e-mail address. In e-mail programs, e- mail address with spaces is considered invalid.

4.      In e-mail programs, e-mail address can be specified in angle brackets, one can also write the recipient's name (in quotes) in front of e-mail address. For example: "Charanjeet Singh" <charanjeetss@gmail.com>.

MAIL FORMAT

·        A mail consists of three parts: an envelope, header and a body (see fig. below).

·        The envelope encapsulates the message and contains all the information needed for transporting the message, such as destination address, priority and security level. This envelope is used by MTAs for routing the message.

·        The header consists of series of lines. Each header field consists of a single line of ASCII text specifying the field name, a colon and the value.

The main header fields related message transport are:

1.      To : specifies the DNS address of primary recipient(s).

2.      Cc : specifies the address of secondary recipient(s). The term Cc refers to the carbon

3.      Bcc : It refers to blind carbon copy. It is similar to Ce : field and is used to specify DNS address of secondary recipients. The only difference is that this line is deleted from all the copies sent to the primary and secondary recipients. Thus, it allows us to send copies to third parties without primary and secondary recipient knowing this.

4.      From : Specifies the name of person who wrote the message.

5.      Sender: Specifies the e-mail address of the person who sent the message. The From : and sender field may specify different values and need not be same.

6.      Received: It is added by each message transfer agent along the way. This field contains the agent's identity, the data and time the message was received and other information that can be used for finding bugs in the routing system.

7.      Return - Path: It is added by the final message transfer agent along the way. This field identity is used to specify how to get back to the sender. This information can also be gathered from all the Received: headers.

The summary of above discussed field is tabulated below:


Header
Meaning
To:
E-mail address primary recipient.
CC:
E-mail address secondary recipient.
Bcc:
E-mail address for bling carbon copies.
From:
Person or people who create the message
Sender:
E-mail address of the actual sender.
Received:
Line added by each transfer agent along the route.
Return-path:
Can be used to identify a path back to sender.







·        In addition to the previously discussed fields, the header may also contain variety of other fields used by the user agents or human recipients. These fields are listed in the table .


Header
Meaning
Date:
Date and time the message was sent.
Reply- to:
E-mail address to which replies should be sent.
Message-id
Unique number for referencing this message later.
In-reply-to :
Message- id of the message to which this is a reply.
References:
Other relevant message id`s.
Keywords:
User-chosen keywords.
Subject:
Short summary of the message for one line display.

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