Winmail.dat Attachment Extractor

Recover files trapped inside an Outlook winmail.dat (TNEF) attachment, without installing a decoder or connecting your mailbox. Send one base64-encoded file and receive an ordered manifest plus downloadable binary attachments in the run's key-value store.

Useful when an email-to-document workflow sees winmail.dat instead of the invoice or other file it expected. This tool extracts bytes; your next step decides what to do with them.

Input and output

Supply {"tnefBase64":"...standard base64 of your file..."}. The example input contains a small synthetic text attachment. For a local file:

import base64, json
from pathlib import Path
print(json.dumps({"tnefBase64": base64.b64encode(Path("winmail.dat").read_bytes()).decode("ascii")}))

In n8n, download the attachment as binary, use Extract from File → Move File to Base64 String, and map that string to tnefBase64 in an Apify Actor call. This workflow recipe has not been executed in n8n Cloud. Use an asynchronous run and wait for SUCCEEDED before reading OUTPUT.

The dataset contains one manifest. files contains index, filename, recordKey, bytes and sha256. Download each recordKey from the run's defaultKeyValueStoreId with your Apify authentication. Files use generated keys such as attachment-001.bin; repeated source filenames cannot overwrite each other. The suggested filename has directories and control characters removed. All binary records use application/octet-stream, so the service does not render their content. Storage access follows your Apify account settings; do not publish confidential run data.

Price

$0.03 per successfully extracted TNEF file, with platform usage included in this pay-per-event price. One event per input file, not per attachment. Malformed, unsupported, over-limit and no-attachment inputs do not incur our extraction event. Successful output is saved before charging. Choose a maximum run charge of at least $0.03. Any platform fees outside this Actor's pricing, and later standalone storage/API use, follow your Apify account plan.

Boundaries

• One decoded file up to 4 MiB, up to 100 attachments, up to 4 MiB total extracted bytes.
• Strict outer attribute lengths and checksums. Parser warnings cause failure instead of silently accepting partial results.
• Byte-preserving extraction with byte counts and SHA-256. This does not verify authenticity or scan for malware.
• No mailbox login, URLs, MSG/EML parsing, decryption, compressed RTF/body conversion, recursive archives or embedded Outlook message extraction. Embedded messages are rejected.
• Bounded parser worker: 10 seconds CPU, 15 seconds wall clock, 256 MiB address-space limit on Linux. Whole-run timeout 60 seconds. Unusual but valid files can be rejected.
• Extraction does not make an attachment safe. Keep your existing scanning/approval steps; do not execute untrusted files.

Validation

26 local tests, including an upstream public fixture, malformed/checksum cases, Unicode filenames, duplicate names and restart charging. Private cloud checks covered small synthetic input, the 4 MiB input limit, corrupt checksum rejection and a cap below the event price. Successful output bytes and hashes were downloaded and verified. These are owner tests, not customer usage or evidence of payment demand. The n8n recipe remains untested in n8n Cloud.

Alternatives and troubleshooting

If you control the sender, changing Outlook to HTML/plain text can eliminate TNEF at the source. For local use, the free tnefparse library and Apache POI HMEF avoid per-run service charges. This Actor is for workflows that prefer a hosted, bounded extraction step using their existing Apify access.

NOT_TNEF: this is not a raw winmail.dat file. INVALID_BASE64: remove data prefixes and use standard base64. BAD_CHECKSUM/TRUNCATED_ATTRIBUTE: obtain a fresh complete attachment. COUNT_LIMIT/INPUT_LIMIT: use a local decoder for larger inputs. UNSUPPORTED_OR_MALFORMED/PARSER_WARNING: the decoder cannot safely accept this file. EMBEDDED_MESSAGE_UNSUPPORTED: use a mail-specific decoder for nested messages. SPENDING_LIMIT: increase the run cap to the advertised single-file price.

Built with unmodified tnefparse 1.4.0 (LGPL-3.0; source and license). A checked compatibility setting enables final empty/one-byte attributes. No comprehensive Outlook-version compatibility claim. Support requests should contain synthetic examples, never confidential mail.

Part of Agent Tools. Workflow examples.