Click this link for details of E-mail Protocols


  • Before 1990, it was mostly used in academia. During the 1990s, it became known to the public at large and grew exponentially to the point where the number of e-mails sent per day now is vastly more than the number of snail mail (i.e. paper letters).
  • The first e-mail systems simply consisted of file transfer protocols, with the convention that the first line of each message (i.e., file) contained the recipient’s address.


  • Electronic mail is also known as e-mail.


  • Electronic mail is one of the most popular tools/services available on the Internet. It is an efficient and effective means of network communication.


  • It is an electronic postal system.
  • It is one of the most valuable and asynchronous(means that the recipient need not be at a computer to receive the message the user sends) ways of communication via email.
  • The message is stored in an e-mail account and available all the time to be read when the recipient is ready to read it.
  • In order to send and receive email, we must have an email account.
  • E-mail, like most other forms of communication, has its own conventions and styles. In particular, it is very informal and has a low threshold of use. Many people also use little ASCII symbols called smileys or emoticons in their e-mail.
  • E-mail is considered full of jargon such as BTW (By The Way), ROTFL (Rolling On The Floor Laughing), and IMHO (In My Humble Opinion). 

Working Mechanism

  • Sending E-mail

    • To send an e-mail message from an e-mail account, a user must provide the message, the destination address, and possibly some other compulsory and optional parameters.

  • Reading E-mail

    • Typically, when a user agent is started up, it looks at the user’s mailbox for an incoming e-mail before displaying anything on the screen. Then it may announce the number of messages in the mailbox or display a one-line summary of each one and wait for a command. 


  • The e-mail structure normally consists of two basic parts or subsystems: (a)The user agents and (b) The message transfer agents

(a) The User Agent

    • A user agent is normally a program (sometimes called a mail reader) that accepts a variety of commands for composing, receiving, and replying to messages, as well as for manipulating mailboxes.
    • This component of e-mail allows people to read and send e-mail.
    • The user agents are local programs that provide a command-based, menu-based, or graphical method for interacting with the e-mail system.
    • Some user agents have a fancy menu- or icon-driven interface that requires a mouse, whereas others expect 1-character commands from the keyboard. Functionally, these are the same. 
Structure of User Agent e-mail:
      • A User Agent has the following email components: –
      • The Compose part is used to write and send email messages to the recipients.
      • It’s important to write clear and concise emails, especially in professional or formal contexts, to ensure that the message is easily understood by the recipient.
      • Additionally, consider the recipient’s preferences and the purpose of the email when structuring and formatting the message.
      • The basic structure of the Compose part of an email consists of several components:-
      1. From:
        • This box contains the sender’s address of the email i.e. it may include our email address, name, and contact details, indicating that we are the sender of the email. 
      2. To:
        • This box contains the email address of the person or group to whom we are sending the email.
        • We can send an email to one or multiple recipients by separating their email addresses with commas or semicolons.
      3. Subject:
        • The subject contains a brief and descriptive summary of the email’s content.
        • It gives recipients an idea of what the email is about and helps them prioritize and organize their emails.
      4. Body:
        • The email body is the main content writing area of our message.
        • It can include text, images, links, emojis, attachments, etc. to clearly and concisely convey our message in the body of the email.
        • Salutation Messages: This is the greeting text at the beginning of the email body. Some common salutations include “Dear [Recipient’s Name],” “Hello [Recipient’s Name],” or simply “Hi.” The choice or ignorance of salutation depends on the formality and familiarity with the recipient.
        • Closing Short Messages: Now, today email agents include some AI features of closing the email message at the end of our body message with common closing short messages such as “Sincerely,” “Best regards,” “Yours truly,” or “Thanks.” We simply choose or ignore a closing short message that suits the tone and formality of our email.
      5. Attachments:
        • This option helps us to attach files, documents, images, or other media in our email if needed.
        • Common attachment formats include PDFs, Word documents, spreadsheets, and image files.
      6. Signature:
        • Now a modern email has an email signature that typically appears at the end of the email and includes our name, contact information, and any other relevant details.
        • Some people also include professional titles or social media links in their signatures.
      7. CC (Carbon Copy) and BCC (Blind Carbon Copy):
        • These fields allow you to include additional recipients in the email.
        • CC recipients are visible to all other recipients, while BCC recipients are hidden from others.
        • This is useful for sending copies or maintaining privacy when emailing multiple parties.
      8. Date and Time Stamp:
        • The date and time when the email was sent are typically displayed at the top of the email.
        • This helps recipients know when the email was composed and sent.
      9. Reply and Forward:
        • Most email clients provide options to reply to or forward an email, allowing them to continue the conversation or share the email with others.
      10. Email Headers:
        • Email headers contain technical information about the email’s routing and delivery, including sender and recipient addresses, message IDs, and server details. These headers are usually hidden from regular email users.


      • The “inbox” is a fundamental component or structure in email systems.
      • It is a specific default folder or location within the email account where all incoming emails are stored.
      • We can also change the Inbox folder to other specific folders or labels.
      • We can access our inbox through our email client or webmail interface software tools.
      • Most email services offer some features to organize the inbox. This includes the ability to create folders or labels, apply filters to automatically sort incoming emails, and mark emails as read or unread.
      • Many email clients use algorithms to automatically categorize or prioritize emails. For example, they might separate promotional emails into a “Promotions” tab or flag important emails as “Priority.”
      • Depending on the email service and preferences, we can archive emails by removing them from the inbox without deleting them.
      • We can mark an email as read or unread.
      • Inboxes often have a search feature that allows one to quickly find specific emails based on keywords, sender, subject, or other criteria.
      • Inboxes often have a search feature that allows us to quickly find specific emails based on keywords, sender, subject, or other criteria.
      • When an Email comes with an attachment our inbox may contain attachments in the forms of documents, images, or files. We can open, download, or save these attachments as needed.
      • Many email clients and mobile apps provide notifications to alert the user when new emails arrive in the inbox. A user can also configure these notifications based on the provided preferences.
      • Some email services have storage limits for our inboxes.
      • Some email clients allow us to set up multiple inboxes or categories to further organize the emails, such as primary, social, and promotions tabs.


      • The “starred” or “flagged” feature in email allows the user to mark specific emails as important or requiring attention.
      • Gmail allows us to make star(*) important emails. We can access all our starred emails by clicking on the “Starred” label in the left sidebar.
      • This feature helps us to prioritize and easily locate important emails among the various messages in our inboxes.
      • To star or flag an email, simply open the email and look for an option like a star icon, flag icon, or a similar symbol, depending on the email service or client. Click or tap on this icon to mark the email as Starred.
      • To remove the star or flag from an email, we can simply click or tap the same icon again. This action typically unmarks the email, indicating that it’s no longer considered important.
      • To find all the emails that are marked as starred or flagged. Simply we can use a search query like “is:starred” or “is:flagged,” followed by any additional search terms if needed.
      • In some email clients, we may have the option to customize the use of stars or flags. This can include using different colors or symbols to represent different levels of importance or priority.
      • Some email clients allow us to set reminders or due dates for flagged emails. This can help us to remember important messages.


      • “Snoozing” in the email refers to a feature that allows us to temporarily remove an email from the inbox and have it reappear at a later time or date.
      • This can be useful for managing the email and ensuring that important messages resurface when we are ready to address them.
      • The snooze feature is helpful for managing our email workflow by allowing it to prioritize messages and deal with them at a more convenient time.
      • The snooze feature is available in many modern email clients and services.
      • To make an email Snooze, open that email and look for the snooze option. It is usually represented by a clock icon or a “Snooze” button in the email client’s interface.
      • To set different types of Snooze options Click or tap on the snooze list, and choose such as “Later today,” “Tomorrow,” “This weekend,” or a custom date and time. By selecting the time or date when we want the email to reappear in our inbox. After choosing a desired snooze time the email will then be removed from the inbox and scheduled to return at the specified time again.
      • Some email clients have a special snooze folder or label where snoozed emails are temporarily stored until they resurface. Others simply hide the email from the main inbox until the snooze period expires.
      • Depending on the email client’s settings, we may receive a notification or reminder when the snoozed email returns to the inbox.
      • Many email clients allow us to customize snooze options, such as setting the preferred snooze times or creating custom snooze intervals.


      • The “Important” or “Priority” option in email allows us to designate certain emails as particularly significant or high-priority.
      • Gmail’s algorithm automatically identifies important emails from all incoming emails and separates them from the rest. We can access all important emails by clicking on the “Important” label in the left sidebar.
      • This feature helps the client to quickly identify and respond to messages that require immediate attention or are crucial to our workflow. 
      • To mark an email as important, open the email and look for an “Important” or “Priority” icon or label in the email client’s interface. Clicking or tapping on this icon usually designates the email as important.
      • To remove the important designation from an email, we can simply click or tap the same icon again. This action typically unmarks the email, indicating that it is no longer considered important.
      • Most email clients provide a dedicated folder, tab, or filter where we can view all the emails marked as important. This makes it easy to locate and prioritize these messages.
      • Depending on the email client tools, we may have the option to customize the use of the “Important” or “Priority” label. For example, we can specify different levels of importance, use colors or icons to represent priority, or define rules that automatically mark certain emails as important based on criteria we set.
      • We can often sort or filter our inbox to display important emails at the top, making it easier to see them first when we access our email account.
      • Some email clients and mobile apps provide notifications that specifically alert us when new important emails arrive in our inboxes.
      • To find all the emails marked as important, simply we use a search query like “is:important” to filter down our results.


      • Sent options of emails are used to manage and track the messages we’ve composed and sent to others.
      • When we send an email, a copy of it is typically saved in our email account’s “Sent” folder or “Sent Items” folder.
      • The sent folder contains a record of all the emails we’ve sent, making it easy to review our sent messages.
      • We can access our sent emails by navigating to the “Sent” folder within our email client or webmail interface.
      • The Sent folder displays a list of our sent messages, including their recipients, subject lines, and timestamps.
      • Some email services offer message tracking features that allow us to see when the recipient opened our sent email or clicked on links within it.
      • We can easily perform various actions on our sent emails using this folder, such as deleting them, moving them to other folders, or marking them as important or starred, depending on our email client’s capabilities.
      • Email clients usually provide a quick and easy search function within the “Sent” folder, enabling us to search for specific sent emails by keywords, recipients, or dates.
      • Some email clients allow us to archive our sent emails, i.e., removing them from the main “Sent” folder but retaining them in an archived location for future reference.


      • The Drafts options are helpful especially when we compose an email but don’t send it immediately, it is often saved in the “Drafts” folder. We can access and edit these draft emails until we’re ready to send them.


      • Scheduled email options of email clients or services allow to compose an email and specify a future date and time for it to be sent automatically.
      • This feature is particularly useful when we want to write an email but don’t want it to be delivered immediately.
      • This service is commonly used for sending birthday wishes, reminders, business work-related emails, or marketing messages at an optimal time.
      • Scheduled email options are also valuable for Time Zone Considerations.
      • This option is available as either labeled “Send Later,” “Schedule Send,” or something similar. After clicking on the scheduling option, we can choose the date and time or choices when we want the email to be sent.
      • Once we’ve scheduled the email, it will be saved in our email client, and we can review or make changes to it before the scheduled send time.
      • As the specified date and time are set, the email client will automatically send the email on my behalf, and it will be delivered to the recipient’s inbox as if I had sent it manually.
      • Most email clients provide a dedicated folder or section where we can view our scheduled emails. This allows us to keep track of emails that are queued for future delivery.
      • We can typically edit or cancel a scheduled email before its send time. If we make changes or decide not to send it, the email won’t be delivered as originally scheduled.


      • This option contains social media content and also enables recipients to interact with or share the email content on social media platforms.
      • These options are often used in marketing and promotional emails to increase the reach and engagement of the email campaign.


      • “Updates options” in email generally refer to features or elements within an email that provide recipients with the latest information or news from a sender.
      • These options are often used in newsletters, subscription emails, event announcements, product updates, social media updates, feedback & survey updates, or notifications to keep recipients informed about specific topics or developments.


      • The forums option within emails can be a useful way to engage recipients and encourage discussions or interactions related to a particular topic or community.
      • Using this, Senders can share highlights from popular or trending forum discussions, ask questions, remind forum members of community guidelines, etiquette, and rules through email updates, or seek advice from the forum community.


      • This option is used to promote products, services, coupon codes, offers, freebies, samples, trials, or events to email subscribers or recipients.
      • These options are commonly employed in marketing emails to drive sales, increase brand awareness, and encourage customer engagement.
      • These emails typically include images, descriptions, prices, and compelling calls to action (CTAs) that encourage recipients to make a purchase or take advantage of the promotion.


      • The “spam option” in email stores unwanted or unsolicited emails, commonly known as spam or junk mail.
      • Managing spam is essential to maintaining a clutter-free and secure email inbox.
      • Email senders can use authentication methods like SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance) to verify their legitimacy. Proper authentication can reduce the likelihood of emails being marked as spam.
      • Email marketers are required to comply with anti-spam laws, such as the CAN-SPAM Act in the United States or the GDPR in the European Union. These laws dictate rules for sending commercial emails and require senders to include opt-out options and accurate sender information.
      • These options are essential for email providers and users to keep their inboxes clean and secure.
      • Most email providers employ spam filters that automatically detect and divert suspected spam emails to a designated spam folder.
      • These filters use various algorithms and rules to assess the likelihood of an email being spam based on factors like sender reputation, content, and user feedback.
      • Email users can mark emails as spam or junk by using the “Report Spam” or “Mark as Junk” option in their email client. When a user marks an email as spam, it helps train the email provider’s spam filter to recognize similar messages in the future.
      • Most email clients have a dedicated spam or junk folder where suspected spam emails are placed. Users can review this folder to ensure that no legitimate emails have been mistakenly classified as spam.


      • The “Trash” or “Deleted Items” folder in our email is a temporary storage location for deleted emails that we have chosen to remove.
      • The Trash folder is designed to give users the safety to recover the last time, deleted items when it is deleted from inbox or other folders accidentally.
      • The retention period for deleted emails in the Trash folder varies depending on the email provider or email client’s settings. In some cases, emails may be automatically deleted from the Trash after a specified period to save storage space, such as 30 days.
      • To recover the deleted items, navigate to the Trash folder, select the email(s) we want to recover, and move them back to the inbox or another folder.
      • To permanently delete emails from the Trash folder, we simply empty the Trash or Deleted Items folder. Once emails are permanently deleted from this folder, they are usually not recoverable. This frees up email storage space and finally increases the email account space.

(o.)Managed Labels:

      • Gmail uses labels instead of creating different types of folders.
      • Each email can have multiple labels as needed. 

(p.)All Mails:

      • All mail labels contain all the emails, including archived ones.


      • When we make an email archive, that email was removed from the inbox but not deleted. It is saved for the future and we can find all our archived emails by clicking on the “All Mail” label or by using search.


      • Gmail Chat integrates with Google Chat, which is part of Google Workspace (formerly G Suite).
      • This feature allows us to have instant messaging conversations with our contacts directly within our Gmail account. 
      • When we’re logged into our Gmail account, look at the left sidebar. You should see a section labeled “Chat.” In the Chat section, we’ll see our contacts listed if we’ve added them to our Google Chat contacts. We can click on a contact’s name to start a chat conversation from here.
      • Google Chat is integrated into Gmail, so we can switch between our emails and chat conversations seamlessly. Clicking on a chat conversation will open a chat window on the right side of our Gmail interface, where we can type and send messages.

(b) The Message Transfer Agent

    • This component of e-mail moves the messages from the source to the destination.
    • The message transfer agents are typically system daemons, that is, processes that run in the background. Their job is to move e-mail through the system.

E-mail Server

  • For email messaging, every domain maintains an email server.
  • A single server can host both the POP and SMTP server programs.
  • The server runs protocol software that enables email communication. There are two main email protocols: POP and SMTP. Because both the email protocol software programs run on server computers, the server computers are themselves called POP servers and SMTP servers. These are –

(i) SMTP server 

    • At the sender’s site, an SMTP server takes the message sent by a user’s computer.
    • The SMTP server at the sender’s end then transfers the message to the SMTP server of the recipient.
    • The SMTP server at the recipient’s end takes the message and stores it in the appropriate user’s mailbox.

(ii) POP server

    • A POP server, short for Post Office Protocol server, is a type of mail server that stores incoming emails for a user until they are downloaded to a client device.
    • It is commonly used for retrieving email messages from an email provider’s server to a local device or email client. 
    • POP3 servers commonly use port 110 for non-encrypted connections or port 995 for encrypted connections (POP3 over SSL/TLS).

E-mail Protocols

Click this Link for Details

Function of E-mail

  • Typically, an e-mail system supports five basic functions: –
    (i) Composition : 
    • It refers to the process of creating messages and answers. Although any text editor can be used for the body of the message, the system itself can provide assistance with addressing the numerous header fields attached to each message.
    • For example, when answering a message, the e-mail system can extract the originator’s address from the incoming e-mail and automatically insert it into the Application Layer’s proper place in the reply.

(ii) Transfer :

    • It refers to moving messages from the originator to the recipient.
    • In large part, this requires establishing a connection to the destination or some intermediate machine, outputting the message, and releasing the connection.
    • The e-mail system should do this automatically, without bothering the user.

(iii) Reporting

    • Reporting has to do with telling the originator what happened to the message. Was it delivered? Was it rejected? Was it lost? Numerous applications exist in which confirmation of delivery is important and may even have legal significance.

(iv) Displaying :

    • In this function, incoming messages are needed so people can read their e-mail. Sometimes the conversion is required or a special viewer must be invoked, for example, if the message is a PostScript file or digitized voice. Simple conversions and formatting are sometimes attempted as well.

(v) Disposition :

    • This is the final step and concerns what the recipient does with the message after receiving it. Possibilities include throwing it away before reading, throwing it away after reading, saving it, and so on. It should also be possible to retrieve and reread saved messages, forward them, or process them in other ways.
    • In addition to these basic services, some e-mail systems, especially internal corporate ones provide a variety of advanced features such as –
      • When people move or when they are away for some period of time, they may want their e-mail forwarded, so the system should be able to do this automatically.
      • Most systems allow users to create mailboxes to store incoming e-mail. Commands are needed to create and destroy mailboxes, inspect the contents of mailboxes, insert and delete messages from mailboxes, and so on.
      • Corporate managers often need to send a message to each of their subordinates, customers, or suppliers. This gives rise to the idea of a mailing list, which is a list of e-mail addresses. When a message is sent to the mailing list, identical copies are delivered to everyone on the list.

Free E-mail Services

  • There are several free email services available today for personal use. 
  • Some popular free email services that are widely used today are as follows:
    • Gmail:
      • Provided by Google, Gmail is one of the most popular free email services.
      • It offers a large amount of storage space, powerful search capabilities, and integration with other Google services.
    • Yahoo Mail:
      • Yahoo Mail is another well-known free email service.
      • It provides features like customizable themes, disposable email addresses, and integration with Yahoo’s news and search services.
    • (formerly called Hotmail):
      • is Microsoft’s free email service.
      • It offers integration with Microsoft Office Online, Skype, and cloud storage through OneDrive.
    • ProtonMail:
      • ProtonMail is known for its strong emphasis on security and privacy.
      • It offers end-to-end encryption for emails and is a good choice for users who prioritize privacy.
    • Zoho Mail:
      • Zoho Mail provides email hosting for personal and business users.
      • It includes features like a calendar, task manager, and integration with other Zoho productivity tools.
    • AOL Mail:
      • AOL Mail is still in use, offering free email services and access to AOL’s news and entertainment content.
      • provides free email addresses with a variety of domain options.
      • It also offers a calendar and cloud storage.
    • GMX Mail:
      • GMX Mail is a free email service with features like a large attachment limit and spam filter.
    • Tutanota:
      • Similar to ProtonMail, Tutanota focuses on secure and private email communication, with end-to-end encryption for all messages.
    • Yandex Mail:
      • Yandex Mail is a free email service from Russia’s Yandex, offering spam protection, a built-in calendar, and cloud storage.

Mailing Lists

  • An Email Mailing List refers to a group or list of email addresses that are used for sending messages to multiple recipients simultaneously.
  • Mailing lists are commonly used for various purposes, including newsletters, announcements, discussions, and collaborative communication.
  • Mailing lists are a valuable tool for online communities, organizations, and businesses to facilitate communication, collaboration, and information sharing among a group of individuals with shared interests or purposes.
  • There are typically two main types of mailing lists: discussion lists and announcement lists.
    1. Discussion Lists:
      • Discussion lists, also known as email discussion groups or email forums, facilitate conversations and discussions among members of the list.
      • When someone sends an email to the mailing list’s address, it is distributed to all members of the list.
      • Members can reply to the entire list or to the sender privately.
      • Discussion lists are often used for professional and hobbyist communities, online forums, and collaborative projects.
    2. Announcement Lists:
      • Announcement lists are designed for one-way communication, where only authorized individuals or organizations can send messages to the list.
      • Subscribers receive announcements, newsletters, updates, or notifications from the list owner.
      • These lists are commonly used for newsletters, company updates, event announcements, and marketing communications.
  • Mailing Lists Working Mechanism:
    • Subscription:

      • To join a mailing list, individuals need to subscribe by providing their email addresses.
      • Some lists may require approval from the list owner or moderator, while others may allow open subscriptions.
    • List Owner/Moderator:

      • Mailing lists are usually managed by a list owner or moderator who oversees the list’s activities.
      • The list owner can control who can subscribe, send messages, and manage the list settings.
    • Sending Messages:

      • To send a message to the mailing list, subscribers use a designated email address (e.g., [email protected]).
      • The message is then distributed to all members of the list.
    • Unsubscribe:

      • Subscribers can typically unsubscribe from a mailing list at any time by following instructions provided in the list’s emails or by contacting the list owner.

    • Archives:

      • Many mailing lists maintain archives of past messages, which are often accessible to subscribers and the public.
      • Archives allow members to search for and reference previous discussions.
    • Privacy:

      • Mailing lists may be public or private.
      • Public lists are open to anyone, while private lists may require approval from the list owner to join.
      • Some lists also offer different levels of privacy, such as allowing only subscribers to view archives.
  • Popular email list management software and services include Mailman, Google Groups, Yahoo Groups (discontinued in 2020), and various mailing list plugins for content management systems (e.g., WordPress).


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