Email Protocols
Email Protocols
Overview
Email communication works using three main protocols:
| Protocol | Purpose |
|---|---|
| SMTP | Sending emails |
| POP3 | Receiving and downloading emails |
| IMAP | Receiving and managing emails on server |
SMTP – Simple Mail Transfer Protocol
Definition
SMTP is a protocol used to SEND emails from a client to a mail server and between mail servers.
Layer
- Application Layer Protocol
- Works over TCP
Port Numbers
| Type | Port |
|---|---|
| Traditional SMTP | 25 |
| SMTPS (SSL) | 465 |
| SMTP with TLS | 587 |
Port 587 is recommended for modern email sending.
Features of SMTP
- Used only for sending emails
- Text-based protocol
- Uses TCP for reliable delivery
- Works in push model (client pushes mail to server)
SMTP Communication Model
User → SMTP Client → SMTP Server → Destination SMTP Server → ReceiverSMTP Commands
| Command | Meaning |
|---|---|
| HELO | Identify client to server |
| MAIL FROM | Sender address |
| RCPT TO | Receiver address |
| DATA | Start message body |
| QUIT | End session |
Limitations of SMTP
- Cannot retrieve emails
- No authentication by default
- Works only for sending
POP3 – Post Office Protocol Version 3
Definition
POP3 is a protocol used to DOWNLOAD emails from mail server to client device.
Port Numbers
| Type | Port |
|---|---|
| POP3 | 110 |
| POP3S (SSL) | 995 |
Characteristics
- Downloads emails to local device
- Usually deletes mail from server after download
- Works in pull model
- Simple and lightweight
POP3 Modes
- Download and Delete – Email removed from server after download
- Download and Keep Copy – Email remains on server
Disadvantages of POP3
- Not suitable for multiple devices
- Limited synchronization
- Emails stored locally only
IMAP – Internet Message Access Protocol
Definition
IMAP is used to ACCESS and MANAGE emails directly on the mail server.
Port Numbers
| Type | Port |
|---|---|
| IMAP | 143 |
| IMAPS (SSL) | 993 |
Advantages of IMAP
- Emails remain on server
- Supports multiple devices
- Folder synchronization
- Better for modern email usage
IMAP vs POP3
| Feature | POP3 | IMAP |
|---|---|---|
| Storage | Local device | Server |
| Sync | No | Yes |
| Multi-device | Poor | Excellent |
| Speed | Faster | Slightly slower |
| Use Case | Single device | Multiple devices |
Protocol Comparison
| Protocol | Function | Default Port |
|---|---|---|
| SMTP | Send emails | 25 / 587 |
| POP3 | Receive and download emails | 110 |
| IMAP | Access and manage emails | 143 |
Quick Revision
- SMTP is used ONLY for sending
- POP3 downloads emails to local device
- IMAP keeps emails on server (best for multiple devices)
- All three work at the Application Layer over TCP