In many interviews, one common question is, "Do you know how email works?"
Understanding this process is crucial, and here's a summary of how it functions. A lot happens when you hit "Send":
Composition:
You write an email using an email client (like Gmail or Outlook).Assembling:
The email client combines the message body with the header (recipient, subject, date).Protocols:
Email uses protocols (SMTP, IMAP, POP) to reach the destination.Types of Clients:
Email clients are either web-based (e.g., Gmail) or client-based (e.g., Outlook).
Email Composition and Sending
Composition:
Emails are written using an email client (e.g., Gmail, Outlook).
The client combines the message body with the header (recipient, subject, date).
Sending:
Upon hitting send, the email is transmitted to an SMTP server.
SMTP (Simple Mail Transfer Protocol) is responsible for handling outgoing mail.
Email Transfer Process
SMTP Server Processing:
The SMTP server identifies the recipient’s domain and performs a DNS (Domain Name System) lookup to find the IP address of the recipient’s mail server.
It checks the MX (Mail Exchange) record to determine where to send the email.
Email Transfer:
The email travels through multiple servers until it reaches the recipient’s SMTP server.
If servers are busy or down, the email may be queued for later delivery.
Email Reception and Retrieval
Reception:
- The recipient’s SMTP server receives the email and stores it in their mailbox.
Retrieval:
The recipient accesses the email using an email client, either via POP3 (Post Office Protocol) or IMAP (Internet Message Access Protocol).
IMAP allows emails to be accessed from multiple devices while remaining on the server.
POP3 typically downloads the email to a single device, possibly removing it from the server.
Email Structure:
Envelope: Contains sender and recipient addresses.
Body: The actual message content, including text, images, and attachments.
Header: Includes essential details like sender, recipient, date, and additional routing information (e.g., the path taken by the email).
Protocols:
SMTP: Used to send emails.
IMAP: Accesses and syncs emails from the server.
POP3: Downloads emails from the server.
IMAP vs. POP3: A Simple Comparison
IMAP (Internet Message Access Protocol):
Synchronization: Emails stay on the server and can be accessed from multiple devices.
Two-Way Communication: Any changes (e.g., reading, deleting) sync across all devices.
Ideal For: Users who access their email from various devices (phones, tablets, computers).
POP3 (Post Office Protocol):
Download and Delete: Emails are downloaded to one device and usually deleted from the server.
One-Way Communication: Actions on one device don't sync with others.
Ideal For: Users who access their email from a single device and need offline access.
In essence, IMAP is more flexible and suitable for multiple devices, while POP3 is simpler and suited for single-device use.
Types of Mail User Agents (MUA):
Email Clients: Installed software like Outlook, Thunderbird.
Webmail: Accessed through browsers like Gmail, Yahoo Mail.
Email Bounces/ Undeliverable Messages:
Permanent Errors (5xx errors):
Invalid Domain: Domain doesn't exist. Example: abc@yordomain.com instead of abc@yourdomain.com. Solution: Correct the domain name.
No MX Records: No mail exchange records found. Solution: Contact recipient’s admin.
Invalid Recipients: Incorrect or non-existent email address. Example: abb@yourdomain.com instead of abc@yourdomain.com. Solution: Check for typos.
Email Policy Violation: Email violates recipient server policies. Example: Sending a .mov attachment when not allowed. Solution: Adhere to policies.
Temporary Errors (4xx errors):
Server Busy: Recipient server is temporarily unavailable. Solution: Wait and retry.
Greylisting: Temporary rejection for new or sudden email sources. Solution: Retry later.
Too Many Emails: Sudden surge causes temporary rejection. Solution: Reduce email volume.
Other Reasons: Full mailbox or anti-spam settings. Solution: Ensure compliance with recipient policies.
Summary of Email Journey:
Send: You hit send, and the email goes to your SMTP server.
SMTP Server: The server looks up the recipient’s domain and gets the IP address via DNS.
Transfer: The email travels through several servers to reach the recipient's MTA(Mail Transfer Agent) server.
Reception: The recipient’s MTA(Mail Transfer Agent) server stores the email until accessed by the recipient.
Retrieval: The recipient uses an email client to access the email, either via POP or IMAP.
Thank You
Hope this helps. Your feedback is appreciated. Please feel free to correct any inaccuracies or provide additional information as needed.
Top comments (0)