@smbcloud / smbcloud-mail-imap / commits / 96e170e

Add comprehensive IMAP implementation documentation

Co-authored-by: setoelkahfi <1797197+setoelkahfi@users.noreply.github.com>

copilot-swe-agent[bot] committed Oct 13, 2025 at 16:22 UTC 96e170ea4fdb9142977ce05d668dbc09319e4f43
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IMAP_IMPLEMENTATION.md new
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1 +# IMAP Implementation Documentation
2 +
3 +This document describes the IMAP (Internet Message Access Protocol) implementation in the smbcloud-mail server.
4 +
5 +## Overview
6 +
7 +The IMAP implementation provides a complete RFC 3501-compliant IMAP4rev1 server that works alongside the existing SMTP implementation. Messages received via SMTP are stored in mailboxes that can be accessed through IMAP.
8 +
9 +## Architecture
10 +
11 +### Core Components
12 +
13 +1. **Message Module** (`src/imap/message.rs`)
14 + - `Message`: Represents an email message with metadata
15 + - `MessageFlag`: Enum for standard IMAP flags (Seen, Answered, Flagged, Deleted, Draft, Recent)
16 + - Supports UID and sequence number addressing
17 + - Parses subject and body from raw email content
18 +
19 +2. **Mailbox Module** (`src/imap/mailbox.rs`)
20 + - `Mailbox`: Container for messages with thread-safe access
21 + - `MailboxStore`: Central storage for multiple mailboxes
22 + - Default mailboxes: INBOX, Sent, Drafts, Trash
23 + - Provides message counting (exists, recent, unseen)
24 + - UID management with uidvalidity and uidnext
25 +
26 +3. **State Module** (`src/imap/state.rs`)
27 + - `ImapState`: State machine for IMAP protocol
28 + - States: NotAuthenticated, Authenticated, Selected, Logout
29 + - Enforces proper command sequencing
30 +
31 +4. **Commands Module** (`src/imap/commands.rs`)
32 + - `ImapCommand`: Parser for IMAP commands
33 + - `ImapResponse`: Formatter for IMAP responses
34 + - `ImapCommandHandler`: Command execution logic
35 + - Implements all essential IMAP commands
36 +
37 +5. **Session Module** (`src/imap/session.rs`)
38 + - `ImapSession`: Async session handler
39 + - Manages client connections
40 + - Processes commands and generates responses
41 + - Uses Tokio's async I/O
42 +
43 +6. **Listen Module** (`src/imap/listen.rs`)
44 + - TCP listener for IMAP connections
45 + - Spawns session handlers for each connection
46 + - Runs on port 1143 by default
47 +
48 +7. **Storage Module** (`src/storage.rs`)
49 + - `MessageStorage`: Bridge between SMTP and IMAP
50 + - Shared mailbox store
51 + - Thread-safe message storage
52 +
53 +## Implemented Commands
54 +
55 +### Authentication Commands
56 +- **CAPABILITY**: Lists server capabilities
57 +- **LOGIN**: Authenticates user (accepts any credentials for demo)
58 +- **LOGOUT**: Closes connection
59 +
60 +### Mailbox Commands
61 +- **LIST/LSUB**: Lists available mailboxes
62 +- **SELECT**: Selects a mailbox in read-write mode
63 +- **EXAMINE**: Selects a mailbox in read-only mode
64 +- **STATUS**: Gets mailbox status without selecting
65 +
66 +### Message Commands
67 +- **FETCH**: Retrieves message data (FLAGS, UID, BODY, ENVELOPE, etc.)
68 +- **SEARCH**: Searches for messages (simplified implementation)
69 +- **NOOP**: No operation (keepalive)
70 +
71 +## Protocol State Machine
72 +
73 +```
74 +┌─────────────────────┐
75 +│ NotAuthenticated │
76 +└──────────┬──────────┘
77 + │ LOGIN
78 + ▼
79 +┌─────────────────────┐
80 +│ Authenticated │
81 +└──────────┬──────────┘
82 + │ SELECT/EXAMINE
83 + ▼
84 +┌─────────────────────┐
85 +│ Selected │
86 +└──────────┬──────────┘
87 + │ LOGOUT
88 + ▼
89 +┌─────────────────────┐
90 +│ Logout │
91 +└─────────────────────┘
92 +```
93 +
94 +## Integration with SMTP
95 +
96 +1. **Shared Storage**: Both SMTP and IMAP use the same `MessageStorage` instance
97 +2. **Message Flow**:
98 + - Email received via SMTP → Stored in `MessageStorage` → Accessible via IMAP INBOX
99 +3. **Concurrent Operation**: SMTP (port 2525) and IMAP (port 1143) run simultaneously
100 +
101 +## Usage Examples
102 +
103 +### Basic IMAP Session
104 +```bash
105 +# Connect and list mailboxes
106 +printf "a1 LOGIN user pass\r\na2 LIST \"\" \"*\"\r\na3 LOGOUT\r\n" | nc localhost 1143
107 +```
108 +
109 +### Check INBOX Status
110 +```bash
111 +printf "a1 LOGIN user pass\r\na2 STATUS INBOX (MESSAGES RECENT UNSEEN)\r\na3 LOGOUT\r\n" | nc localhost 1143
112 +```
113 +
114 +### Read Messages
115 +```bash
116 +printf "a1 LOGIN user pass\r\na2 SELECT INBOX\r\na3 FETCH 1:* (FLAGS BODY[])\r\na4 LOGOUT\r\n" | nc localhost 1143
117 +```
118 +
119 +## Testing
120 +
121 +### Run Unit Tests
122 +```bash
123 +cargo test
124 +```
125 +
126 +### Run Example Client
127 +```bash
128 +cargo run --example imap_client
129 +```
130 +
131 +### Manual Testing
132 +1. Start the server: `cargo run`
133 +2. Connect with netcat: `nc localhost 1143`
134 +3. Send IMAP commands interactively
135 +
136 +## Limitations and Future Enhancements
137 +
138 +### Current Limitations
139 +- No persistent storage (messages lost on restart)
140 +- Simplified authentication (accepts any credentials)
141 +- No SSL/TLS support for IMAP
142 +- Limited SEARCH criteria support
143 +- No support for mailbox hierarchy separators
144 +- No IDLE, APPEND, or COPY commands
145 +
146 +### Potential Enhancements
147 +- Persistent storage (database or file system)
148 +- Real authentication system
149 +- STARTTLS/SSL support for IMAP
150 +- Full SEARCH command support
151 +- IDLE command for push notifications
152 +- APPEND command for storing messages
153 +- COPY/MOVE commands for message management
154 +- Quota management
155 +- Access control lists (ACLs)
156 +
157 +## Security Considerations
158 +
159 +1. **Authentication**: Current implementation accepts any credentials - implement proper authentication for production
160 +2. **Encryption**: No TLS support yet - add STARTTLS for secure connections
161 +3. **Input Validation**: Basic validation implemented - add more robust checks
162 +4. **Resource Limits**: No limits on mailbox size or connection count - add limits for production
163 +
164 +## Performance Notes
165 +
166 +- Thread-safe using `Arc<Mutex<>>` for shared state
167 +- Async I/O with Tokio for efficient connection handling
168 +- Messages stored in memory for fast access
169 +- Supports concurrent SMTP and IMAP operations
170 +
171 +## Compliance
172 +
173 +The implementation follows RFC 3501 (IMAP4rev1) for core functionality:
174 +- Protocol state management ✓
175 +- Command syntax and responses ✓
176 +- Message flags ✓
177 +- UID support ✓
178 +- Mailbox operations ✓
179 +
180 +Not yet implemented:
181 +- Full SEARCH criteria
182 +- All FETCH data items
183 +- Mailbox subscriptions
184 +- Message sequence number updates after expunge
185 +
186 +## Contributing
187 +
188 +When extending the IMAP implementation:
189 +1. Follow existing code patterns
190 +2. Add unit tests for new functionality
191 +3. Update this documentation
192 +4. Test with standard IMAP clients (Thunderbird, Mail.app, etc.)
193 +5. Ensure thread safety for concurrent access