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Aspose.Email FOSS for .NET

Read, create, and process Outlook MSG files, CFB containers, and EML messages from .NET — free and open-source, no Microsoft Outlook dependency.

Aspose.Email FOSS for .NET for .NET Aspose.Email FOSS for .NET
for .NET

Documentation GitHub

Open-Source .NET Library for MSG, CFB, and EML Files

Aspose.Email FOSS for .NET is a MIT-licensed, dependency-free C# library for working with Microsoft Outlook .msg files, Compound File Binary (CFB) containers, and EML messages. Add a single NuGet package and immediately start reading, creating, and processing email messages without installing Microsoft Outlook or any proprietary runtime.

The library provides two levels of access. At the low level, CfbReader and CfbWriter give full control over CFB binary containers — traverse directory entries, read and write storage nodes and stream data, and inspect the raw sector layout. MsgReader and MsgWriter handle the MSG format on top of CFB, exposing MAPI property streams, recipient tables, and attachment sub-storages. At the high level, MapiMessage lets you create new messages from scratch, read subject, body, sender, and recipients, manage attachments, and convert between MSG and EML format via a built-in MIME implementation.

The library targets .NET 8.0 or later and has no native dependencies, making it suitable for Windows, Linux, macOS, Docker containers, and serverless functions.

CFB Container Read and Write

  • Open CFB files: Load existing CFB containers from a file path, stream, or byte array via CfbReader.FromFile(), CfbReader.FromStream(), or new CfbReader(data).
  • Traverse the directory tree: Iterate storages, streams, and children using IterStorages(), IterStreams(), IterChildren(), and IterTree().
  • Resolve paths: Navigate nested storage hierarchies with ResolvePath(names) to locate a specific stream by name chain.
  • Write CFB containers: Build CFB documents programmatically with CfbDocument and serialize to bytes or file via CfbWriter.ToBytes() or CfbWriter.WriteFile().
  • Add storages and streams: Attach CfbStorage and CfbStream nodes to any storage node before serialization.

Where CFB Access Is Used

  • MSG file inspection: CFB is the container format for Outlook .msg files — direct CFB access enables forensic inspection and repair.
  • Custom binary formats: Any legacy application using CFB for data storage can be read or written without a COM dependency.
  • Data recovery: Traverse the full directory tree and extract raw stream bytes from damaged or non-standard CFB files.
  • Binary round-trip testing: Serialize a document to bytes and reload it to verify lossless serialization in automated tests.

MSG File Read and Write

  • Read MSG files: Open Outlook MSG files with MsgReader.FromFile() or MsgReader.FromStream() and access the underlying MAPI property streams, recipient records, and attachment sub-storages.
  • Write MSG files: Produce MSG files from a MsgDocument with MsgWriter.ToBytes() or MsgWriter.WriteFile().
  • Low-level MAPI access: Read top-level property streams, named properties, and attachment data via MsgStorage, MsgStream, and MsgReader.ParseTopLevelPropertyStream().
  • MSG storage navigation: Use MsgStorage.FindStream() and MsgStorage.FindStorage() to locate named sub-entries.

Where MSG Processing Is Used

  • Email archival pipelines: Bulk-read .msg files from archive directories and extract metadata or attachments.
  • Migration tools: Convert MSG collections to standard formats for import into non-Outlook systems.
  • Legal discovery: Parse raw MAPI property streams to extract all message fields including non-standard properties.
  • Automated report delivery: Construct .msg files programmatically and deliver them to Outlook-based mail systems.

High-Level Message API

  • Create messages: Build a complete email with MapiMessage.Create(subject, body), set SenderName, SenderEmailAddress, and HtmlBody.
  • Add recipients: Attach To, Cc, and Bcc recipients via AddRecipient() with email address and display name.
  • Manage attachments: Add file and stream attachments with AddAttachment() or construct MapiAttachment objects directly with Filename, MimeType, ContentId, and Data.
  • Save and reload: Serialize with message.Save() or message.Save(stream) and reload with MapiMessage.FromFile() or MapiMessage.FromStream().

Where the High-Level API Is Used

  • Automated email generation: Generate thousands of personalized MSG files from data records in batch jobs.
  • Test fixture creation: Build known-good MSG files with predictable content for integration test suites.
  • Attachment extraction: Load an MSG file, iterate message.Attachments, and save each attachment.Data to disk.
  • Property inspection: Access message.Subject, message.Body, message.SenderEmailAddress, and message.Recipients without COM automation.

EML and MIME Conversion

  • Load EML into MapiMessage: Parse a standard .eml file (RFC 5322 / MIME) into a full MapiMessage object via MapiMessage.LoadFromEml(stream).
  • Save MapiMessage as EML: Serialize a MapiMessage back to MIME format with message.SaveToEml() or message.SaveToEml(stream).
  • Round-trip fidelity: Subject, body, HTML body, sender, recipients, and attachments are all preserved through EML → MSG → EML round-trips.
  • No external MIME parser: EML parsing is implemented natively within the library — no System.Net.Mail dependency required.

Where EML Conversion Is Used

  • Format bridging: Receive emails as EML from mail servers and convert to MSG for Outlook-compatible storage.
  • Standards compliance: Convert proprietary MSG files to standard MIME for delivery to any mail transport.
  • Archival normalization: Normalize a mixed archive of .eml and .msg files to a single format.
  • Testing workflows: Generate .eml fixtures in tests and verify they survive MSG round-trip without data loss.

Read Subject from an MSG File

Open an Outlook MSG file from a stream and print the subject — no Microsoft Outlook required.

using System.IO;
using Aspose.Email.Foss.Msg;
using var stream = File.OpenRead("sample.msg");

var message = MapiMessage.FromStream(stream);
Console.WriteLine(message.Subject);

Create and Save an MSG Message

Build a complete email with sender, recipient, and attachment, then write it to an MSG file.

using System.IO;
using Aspose.Email.Foss.Msg;

var message = MapiMessage.Create("Hello", "Body");
message.SenderName = "Alice";
message.SenderEmailAddress = "alice@example.com";
message.AddRecipient("bob@example.com", "Bob");
using var attachmentStream = new MemoryStream("abc"u8.ToArray());
message.AddAttachment("note.txt", attachmentStream, "text/plain");
using var output = File.Create("hello.msg");
message.Save(output);

Convert EML to MSG

Load a standard .eml file and save it as an Outlook .msg file using the built-in MIME parser.

using System.IO;
using Aspose.Email.Foss.Msg;
using var input = File.OpenRead("message.eml");

var message = MapiMessage.LoadFromEml(input);
using var msgOutput = File.Create("message.msg");
message.Save(msgOutput);
using var emlOutput = File.Create("roundtrip.eml");
message.SaveToEml(emlOutput);