📧 SMTP (Simple Mail Transfer Protocol)
SMTP (Simple Mail Transfer Protocol) is the standard protocol used for sending emails over the internet.
👉 Important:
SMTP → Used to SEND emails
IMAP / POP3 → Used to RECEIVE emails🔹 What is SMTP?
SMTP is an application layer protocol that transfers outgoing mail from:
Sender’s email client → Mail server
Mail server → Recipient’s mail serverIt does not retrieve emails. It only handles sending.
🔹 How SMTP Works (Simple Flow)
User composes email.
Email client connects to SMTP server.
SMTP server sends mail to recipient's mail server.
Recipient retrieves mail using IMAP or POP3.
🔹 SMTP Port Numbers
| Type | Port Number |
|---|---|
| Default SMTP | 25 |
| SMTP with SSL | 465 |
| SMTP with TLS (STARTTLS) | 587 |
📌 Exam Tip:
Port 25 → Traditional SMTP
Port 587 → Modern secure email submission
🔹 Key Features of SMTP
Used only for sending emails
Works on TCP protocolText-based protocol
Requires authentication for security
Works with IMAP or POP3 for complete email system
🔹 SMTP vs IMAP vs POP3 (Quick Comparison)
| Feature | SMTP | IMAP | POP3 |
|---|---|---|---|
| Purpose | Sending emails | Receiving emails | Receiving emails |
| Sync | No | Yes | No |
| Default Port | 25 | 143 | 110 |
| Secure Port | 465 / 587 | 993 | 995 |
📘 SMTP MCQs (Exam Oriented)
1. SMTP is used for:
A) Receiving emails
B) Sending emails
C) File transfer
D) Web browsing
✅ Answer: B) Sending emails
2. SMTP stands for:
A) Simple Mail Transfer Protocol
B) Secure Mail Transfer Process
C) System Mail Transfer Protocol
D) Simple Message Transport Program
✅ Answer: A) Simple Mail Transfer Protocol
3. Default port number of SMTP is:
A) 110
B) 143
C) 25
D) 993
✅ Answer: C) 25
4. SMTP works at which layer of OSI model?
A) Transport Layer
B) Network Layer
C) Application Layer
D) Data Link Layer
✅ Answer: C) Application Layer
5. Which protocol is used along with SMTP to receive emails?
A) FTP
B) IMAP / POP3
C) HTTP
D) TCP
✅ Answer: B) IMAP / POP3
🎯 Important Exam Summary
✔ SMTP → Sending
✔ IMAP → Server-based Receiving
✔ POP3 → Local Receiving
✔ Port 25 → SMTP
✔ Port 587 → Secure Email Submission
✔ Application Layer Protocol