OneMail · onemail docs · Recursive AI

An email library for .NET with no dependency beyond the .NET base class library and its sibling libraries (OneArchive, OneHtml, OneRender). It reads and writes the formats mail lives in, keeps what it reads lossless, and says what it repaired instead of throwing.

Early preview. MIME, the mailbox stores, ICS/vCard trees with recurrence and time zones, and Outlook items on read (MSG/OFT, PST/OST, TNEF, compressed RTF, MAPI↔MIME conversion) work today; Outlook writing, protocols and cryptography are still to come. Nothing here is a stable API yet. What is checked, and the known gaps: docs/compatibility.md.

using RecursiveAI.OneMail;
 
IMailItem message = Mail.Parse(File.ReadAllBytes("message.eml"));
Console.WriteLine($"{message.Subject} from {message.From[0].Address}");
 
using MailContainer mbox = Mail.Open("archive.mbox");
foreach (IMailItem item in mbox.Enumerate())
{
    Console.WriteLine(item.Subject);
}

Goals

Reads: MIME/EML, MHTML, TNEF, MSG/OFT, PST and OST, MBOX variants, Maildir, EMLX, OLM, DBX, ICS and vCard (and their JSON/XML forms).
Writes: the exchange formats, MSG/OFT and Unicode PST.
Lossless and lenient: untouched MIME, ICS and vCard write back byte for byte; Outlook data round-trips property for property; every repair of malformed input is a typed defect with its byte offset.
Every layer public: random-access sources, the MIME reader and writer, the PST layers and the raw protocol layer, with a one-line happy path on top.
Protocols and cryptography in separate packages: SMTP, IMAP, POP3, SASL; DKIM, ARC, S/MIME and OpenPGP.
NativeAOT, trimming and browser WebAssembly (format core) are supported targets from the start.

Packages

All packages target net10.0 and share one version. RecursiveAI.OneMail, RecursiveAI.OneMail.Calendar and RecursiveAI.OneMail.Cli are on NuGet (0.2.0-preview.2); .Client, .Cryptography and .Render are not published yet.

Package	Contents	Depends on
`RecursiveAI.OneMail.Calendar`	ICS, vCard, JSON/XML forms, recurrence, time zones	.NET only
`RecursiveAI.OneMail`	the formats, the models and the one-line entry points	`.Calendar`, `RecursiveAI.OneArchive`, `RecursiveAI.OneHtml`
`RecursiveAI.OneMail.Client`	SMTP, IMAP, POP3, SASL and the raw protocol layer	`RecursiveAI.OneMail`
`RecursiveAI.OneMail.Cryptography`	DKIM, ARC, S/MIME, OpenPGP	`RecursiveAI.OneMail`
`RecursiveAI.OneMail.Render`	a message to PDF or an image	`RecursiveAI.OneMail`, `RecursiveAI.OneRender`
`RecursiveAI.OneMail.Cli`	the `onemail` command-line tool	`RecursiveAI.OneMail`

Clean room

OneMail is written from public specifications (RFCs, Microsoft's Open Specifications, WHATWG) and from observing released programs as black boxes. The source of other mail libraries is not read.

Not affiliated

This project is unaffiliated with other products named OneMail.

Building

See CONTRIBUTING.md.

Licence

MIT OR Apache-2.0, at your option: LICENSE-MIT, LICENSE-APACHE. Copyright (c) Recursive AI, LLC.