SwiftMail

A Swift package for comprehensive email functionality, providing robust IMAP and SMTP client implementations.

Overview

SwiftMail is a powerful email package that enables you to work with email protocols in your Swift applications. The package provides two main components:

IMAPServer

Handles IMAP server connections for retrieving and managing emails. Implements key IMAP capabilities including:

• Mailbox operations (SELECT, LIST, COPY, MOVE)
• Message operations (FETCH headers/parts/structure, STORE flags) with automatic chunking for large sets
• Special-use mailbox support
• Creating new messages via APPEND (draft-friendly)
• Namespace-aware mailbox resolution (NAMESPACE)
• Extended search with structured results (ESEARCH)
• Append size preflight checks (APPENDLIMIT)
• TLS encryption
• UID-based operations via UIDPLUS

📊 IMAP Capability Support: Gmail vs iCloud vs Dovecot vs Exchange vs IMAPServer

The table below compares common IMAP capabilities across Gmail, iCloud, Dovecot, Exchange, and SwiftMail's IMAPServer. NIOIMAP indicates capability/command/parser support present in the underlying swift-nio-imap grammar layer. The final column indicates whether IMAPServer implements support for each capability.

IMAP Capability	Description	Gmail	iCloud	Dovecot	Exchange	NIOIMAP	IMAPServer
IMAP4rev1	Standard IMAP protocol (RFC 3501)	✅	✅	✅	✅	✅	✅
UNSELECT	Unselect mailbox without selecting another (RFC 3691)	✅	✅	✅	✅	✅	✅
IDLE	Push new message alerts (RFC 2177)	✅	✅	✅	✅	✅	✅
NAMESPACE	Query folder structure roots (RFC 2342)	✅	✅	✅	✅	✅	✅
QUOTA	Storage quota reporting (RFC 2087)	✅	✅	✅	❌	✅	✅
ID	Identify client/server (RFC 2971)	✅	✅	✅	✅	✅	✅
XLIST	Gmail folder role mapping (legacy)	✅	❌	❌	❌	❌	❌
CHILDREN	Show folder substructure (RFC 3348)	✅	❌	✅	✅	✅	✅
X-GM-EXT-1	Gmail labels, threads, msg IDs	✅	❌	❌	❌	✅	❌
UIDPLUS	Enhanced UID operations (RFC 4315)	✅	✅	✅	✅	✅	✅
COMPRESS=DEFLATE	zlib compression (RFC 4978)	✅	❌	❌	❌	✅	❌
ENABLE	Enable optional extensions (RFC 5161)	✅	✅	✅	❌	✅	✅
MOVE	Native IMAP MOVE command (RFC 6851)	✅	❌	✅	✅	✅	✅
CONDSTORE	Efficient state sync (RFC 7162)	✅	✅	✅	❌	✅	❌
ESEARCH	Extended search (RFC 4731)	✅	✅	✅	❌	✅	✅
UTF8=ACCEPT	UTF-8 folder & header support (RFC 6855)	✅	❌	❌	❌	❌	❌
LIST-EXTENDED	Advanced mailbox listing (RFC 5258)	✅	❌	✅	❌	✅	❌
LIST-STATUS	List + status in one (RFC 5819)	✅	✅	✅	❌	✅	❌
LITERAL-	Literal string optimization (RFC 7888)	✅	❌	❌	❌	✅	❌
SPECIAL-USE	Modern folder role marking (RFC 6154)	✅	❌	✅	❌	✅	✅
APPENDLIMIT=…	Message size limit for uploads	✅	❌	❌	❌	✅	✅
QRESYNC	Quick resync via SELECT (RFC 7162)	❌	✅	✅	❌	✅	✅
SORT	Server-side message sorting (RFC 5256)	❌	✅	✅	❌	❌	❌
ESORT	Extended SORT results (RFC 5267)	❌	✅	✅	❌	❌	❌
CONTEXT=SORT	Persistent sort context	❌	✅	❌	❌	❌	❌
WITHIN	Search by relative time (RFC 5032)	❌	✅	✅	❌	✅	✅
SASL-IR	Initial SASL response support (RFC 4959)	❌	✅	✅	✅	✅	✅
XAPPLEPUSHSERVICE	Apple push integration for Mail app	❌	✅	❌	❌	❌	❌
XAPPLELITERAL	Apple literal transmission optimization	❌	✅	❌	❌	❌	❌
X-APPLE-REMOTE-LINKS	Apple-specific remote links extension	❌	✅	❌	❌	❌	❌

SwiftMail supports explicit enable(_:) calls and QRESYNC SELECT with a stored UIDVALIDITY and modification-sequence checkpoint. The result includes mailbox metadata, historical and live vanished UIDs, and complete flag replacements. QRESYNC EXAMINE, optional known-UID and sequence-match parameters, and the VANISHED UID FETCH modifier are not exposed. See Resynchronizing with QRESYNC for enablement, checkpoint validation, and fallback guidance.

Exchange source (captured 2026-03-05 from outlook.office365.com:993 via IMAPS CAPABILITY):

* CAPABILITY IMAP4 IMAP4rev1 AUTH=PLAIN AUTH=XOAUTH2 SASL-IR UIDPLUS MOVE ID UNSELECT CHILDREN IDLE NAMESPACE LITERAL+

SMTPServer

Handles email sending via SMTP with support for:

• Multiple authentication methods (PLAIN, LOGIN, XOAUTH2)
• TLS encryption
• 8BITMIME support
• Full MIME email composition
• Multiple recipients (To, CC, BCC)

Command Line Demos

The package includes command line demos that showcase the functionality of both the IMAP and SMTP libraries:

• SwiftIMAPCLI: Demonstrates IMAP operations like listing mailboxes and fetching messages
• SwiftSMTPCLI: Demonstrates sending emails via SMTP

Both demos look for a .env file in the current working directory for configuration. Create a .env file with the following variables:

# IMAP Configuration
IMAP_HOST=imap.example.com
IMAP_PORT=993
IMAP_USERNAME=your_username
IMAP_PASSWORD=your_password

# SMTP Configuration
SMTP_HOST=smtp.example.com
SMTP_PORT=587
SMTP_USERNAME=your_username
SMTP_PASSWORD=your_password

Note for Gmail Users: When using Gmail, you cannot authenticate with your Google account password. Instead, you must create an app-specific password and use that as your password in the configuration above.

To run the demos:

# Run the IMAP demo
swift run SwiftIMAPCLI

# Run the SMTP demo
swift run SwiftSMTPCLI

# Run with debug logging enabled (recommended for development)
ENABLE_DEBUG_OUTPUT=1 OS_ACTIVITY_DT_MODE=debug swift run SwiftIMAPCLI
ENABLE_DEBUG_OUTPUT=1 OS_ACTIVITY_DT_MODE=debug swift run SwiftSMTPCLI

The debug logging options:

• ENABLE_DEBUG_OUTPUT=1: Enables trace level logging
• OS_ACTIVITY_DT_MODE=debug: Formats debug output in a readable way

Creating Drafts via IMAP

SwiftMail lets you build a draft with the shared Email model (also used by SMTP) and store it directly on the server:

let draft = Email(
    sender: EmailAddress(name: "Me", address: "me@example.com"),
    recipients: [],
    subject: "Quarterly update",
    textBody: "Jot down your notes here…"
)

let appendResult = try await imapServer.createDraft(from: draft)
if let uid = appendResult.firstUID {
    print("Draft stored with UID \(uid.value)")
}

Need a custom target mailbox or additional flags? Use the lower-level helper:

try await imapServer.append(
    email: draft,
    to: "Archive/Drafts",
    flags: [.seen]
)

Requirements

• Swift 5.9+
• macOS 11.0+
• iOS 14.0+
• tvOS 14.0+
• watchOS 7.0+
• macCatalyst 14.0+

Dependencies

• SwiftNIO
• SwiftNIOSSL
• SwiftNIOIMAP (for IMAP only)
• SwiftDotenv (for CLI demos)
• Swift Testing (for tests only)
• Swift Logging

License

This project is licensed under the BSD 2-Clause License - see the LICENSE file for details.