Read PST and OST Files in .NET Without Outlook

OfficeIMO.Email opens Outlook PST and OST files plus OLM, mbox, EMLX, Apple Mail, Maildir, and mailbox directories without Outlook, COM, or a hosted conversion service. The same store API returns ordinary EmailDocument objects while retaining folder paths, associated items, diagnostics, and bounded attachment access.

Read a PST or OST

using System.Linq;
using OfficeIMO.Email.Store;

using EmailStoreSession session = EmailStoreSession.Open("archive.ost");

foreach (EmailStoreItemReference reference in session.EnumerateItems(
    new EmailStoreEnumerationOptions(maxItems: 10_000))) {
    EmailStoreItem item = session.ReadItem(reference);
    string folderPath = string.Join("/",
        session.FolderCatalog.GetPath(reference.FolderKey).Select(folder => folder.Name));
    Console.WriteLine($"{folderPath}: {item.Document.Subject}");
}

Set item, attachment, total attachment, and input limits for untrusted or unusually large stores. Subjects and other message values are data, not safe output paths.

Convert OST, OLM, mbox, or Maildir to PST

Conversion writes a new PST. It does not repair or rewrite the source store in place.

using EmailStoreSession source = EmailStoreSession.Open("mailbox.ost");

EmailStorePstConversionReport report = source.ExportToPst(
    "mailbox-export.pst",
    new EmailStorePstConversionOptions(
        continueOnItemError: true,
        includeAssociatedItems: true,
        includeOrphanedItems: true));

Console.WriteLine($"Converted: {report.ConvertedItems}");
Console.WriteLine($"Skipped: {report.SkippedItems}");
Console.WriteLine($"Verified: {report.Verification?.IsSuccessful}");

The report separates converted and skipped items. Optional keyed semantic fingerprints can compare the source and destination without placing subjects, addresses, body text, or attachment names in the verification manifest.

Choose the right output

Mailbox semantics vary across stores. Associated items, recurrence, RTF bodies, TNEF, embedded messages, address books, and damaged records need representative fixtures and explicit acceptance rules.

Continue with mailbox stores, email safety and verification, or the Email API reference.