MBOX Mailbox (three-message thread)
An mbox mailbox concatenating a short three-message email thread with the classic 'From ' separator lines and >From body escaping — for testing mailbox splitting and thread reconstruction.
From maya@brightside.example Thu Jan 15 09:30:00 2026
Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: base64
From: Maya Chen <maya@brightside.example>
To: Sam Rivera <sam@meridiansupply.example>
Subject: Your quote Q-2026-0148
Date: Thu, 15 Jan 2026 09:30:00 -0800
Message-ID: <t1@brightside.example>
SGkgU2FtLAoKQ291bGQgeW91IHNlbmQgYSBxdW90ZSBmb3Igb3VyIG1vbnRobHkgc3VwcGxpZXMg
b3JkZXI/CgpUaGFua3MsCk1heWEK
From sam@meridiansupply.example Thu Jan 15 09:30:00 2026
Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: base64
From: Sam Rivera <sam@meridiansupply.example>
To: Maya Chen <maya@brightside.example>
Subject: Re: Your quote Q-2026-0148
Date: Thu, 15 Jan 2026 11:05:00 -0800
Message-ID: <t2@brightside.example>
SGkgTWF5YSwKCkF0dGFjaGVkIGlzIHF1b3RlIFEtMjAyNi0wMTQ4LiBJdCdzIGhlbGQgZm9yIDMw
IGRheXMuCgpTYW0K
From maya@brightside.example Thu Jan 15 09:30:00 2026
Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: base64
From: Maya Chen <maya@brightside.example>
To: Sam Rivera <sam@meridiansupply.example>
Subject: Re: Your quote Q-2026-0148
Date: Thu, 15 Jan 2026 13:40:00 -0800
Message-ID: <t3@brightside.example>
UGVyZmVjdCwgd2UnbGwgY29uZmlybSBzaG9ydGx5LiBUaGFua3MhCk1heWEK
Specifications
- Format
- mbox (mboxo)
- Messages
- 3
- Separators
- 'From ' lines
- Escaping
- >From
What is a .mbox file?
An MBOX file is a mailbox that stores many email messages concatenated into one plain-text file, each message preceded by a 'From ' separator line. It is the classic Unix mailbox format used by many mail clients for export and archival.
How to use this file
Use an example MBOX to test mailbox splitting, message boundary detection, thread reconstruction, and import into a mail client or parser.
How to use this file for testing
“MBOX Mailbox (three-message thread)” is a deterministic Novus Examples fixture for Email parsing, Conversion testing. Standards-compliant RFC 822 messages — plain, multipart text+HTML, and with an attachment — plus an MBOX mailbox, for testing header parsing, MIME decoding, attachment extraction, and mailbox splitting.
Documented properties for this file: 3 messages · mbox (mboxo). Compare results against paired or grouped companions on this page when present (clean↔damaged, searchable↔scanned, or format twins) so scores stay reproducible across runs.
Download the file once, keep the path stable in CI or local scripts, and treat the spec table as the contract: dimensions, seeds, field lists, and roles are intentional. Corrupt or invalid samples are labelled as such — expect parsers to fail loudly rather than silently accept them.
Email fixtures use fixed dates, message IDs, and MIME boundaries so runs are reproducible, and every address is fictional. Test header parsing, MIME decoding, attachment extraction, and EML/MBOX conversion against the documented structure.
Code examples
import mailbox
for msg in mailbox.mbox("thread.mbox"):
print(msg["subject"])Related files
- emlEmail with Attachment (EML)A multipart/mixed email with a base64-encoded CSV file attachment — for testing attachment detection, decoding, and extraction from an EML message.
- emlMultipart Email — Text + HTML (EML)A multipart/alternative email carrying both a plain-text and an HTML body — for testing MIME part selection, HTML-part handling and sanitising, and multipart parsing.
- emlPlain-Text Email (EML)A standards-compliant plain-text email message (.eml) with full headers — the simplest valid RFC 822 message for testing email header parsing and EML import.
- emlBounce / Non-Delivery Report (EML)A bounce / non-delivery report (NDR) — a multipart/report message with a human-readable notice, a message/delivery-status part, and the original headers — for testing bounce parsing and delivery-status extraction.
- emlEML — 1,024-Octet Header Line With No Fold PointA single header whose value is one 1,001-character token with no whitespace, making the line 1,024 octets — past the 998-octet limit RFC 5322 sets and impossible to fold. Fixed-size line buffers truncate here, and the truncation is silent.
- emlEML — Attachment With No Filename At AllAn attachment with a bare Content-Disposition: attachment and no name in either header. A client has to invent a filename, and the extension it invents decides whether the saved file opens as a spreadsheet or as unknown binary.
Generated by generation/email_samples.py. Free for any use, no attribution required — license.