Skip to main content

Documentation Index

Fetch the complete documentation index at: https://mintfax.com/docs/llms.txt

Use this file to discover all available pages before exploring further.

​
Glossary

Protocol specs, telephony jargon, compliance acronyms, and API concepts that appear throughout the mintfax documentation. Each entry has a stable anchor (e.g., /glossary#t30) that other pages link to.

​
BAA

Business Associate Agreement. A contract required under HIPAA between a covered entity (healthcare provider, insurer, clearinghouse) and a business associate that handles PHI on its behalf. The BAA defines each party’s obligations for safeguarding protected health information. mintfax signs a BAA with customers on paid plans at no additional cost. See also

​
Conduit exception

A HIPAA provision that excludes entities acting as mere conduits for PHI from Business Associate requirements. A conduit transmits information but does not access it beyond what transmission requires. Whether a fax API provider qualifies depends on access to fax content, storage duration, and ability to view document contents. mintfax’s zero-footprint mode and encryption design support the conduit characterization, but each customer should evaluate their own compliance posture. See also

​
Cover page

A generated first page prepended to a fax that typically includes sender name, recipient name, subject, and page count. mintfax cover page settings are configurable per fax or at the workspace level. See also

​
DID

Direct Inward Dialing number. A telephone number assigned to a fax line or endpoint without requiring a dedicated physical line. DIDs are the numbers that appear in fax headers and that callers dial to reach a fax machine or service. Written in E.164 format: +12015550100. See also

​
ECM

Error Correction Mode. An optional T.30 capability that adds error detection and retransmission at the protocol level. When both sides support ECM, pages are transmitted in frames with checksums, and corrupted frames are retransmitted before the page is accepted. ECM improves image quality on noisy lines at the cost of longer transmission time. See also

​
Fax

A method of transmitting documents over telephone networks. The sending device scans a page, encodes the image, and transmits it as audio tones (G3) or data packets (T.38) to a receiving device that reconstructs and prints or stores the image. In the mintfax API, a fax is the core resource. It has an id field and moves through statuses: queued, submitted, in_progress, delivered, failed. See also

​
FoIP

Fax over IP. The umbrella term for technologies that send faxes over IP networks instead of traditional PSTN circuits. FoIP includes T.38 (a dedicated real-time fax relay protocol) and G.711 pass-through (encoding fax tones as audio in a voice codec). Most modern fax infrastructure runs on some form of FoIP. See also

​
G3

Group 3 fax. The dominant fax standard, defined by the ITU-T T.30 recommendation. G3 machines communicate using audio-frequency tones over voice-grade telephone channels. They negotiate capabilities (speed, compression, ECM) through a handshake before transmitting page data. Nearly all fax traffic today is G3. See also

​
G.711

An ITU-T audio codec that digitizes voice (and fax tones) at 64 kbps. In fax contexts, G.711 pass-through carries the analog fax signal as a voice call over VoIP. Simpler than T.38, but more sensitive to packet loss and jitter because the receiving end must decode the audio tones back into fax data. See also

​
HMAC signature

Hash-based Message Authentication Code. mintfax signs every webhook payload with HMAC-SHA256 using a per-account signing secret. The receiving server recomputes the hash from the raw payload and compares it to the signature in the request headers to verify the payload came from mintfax and was not altered in transit. See also

​
Idempotency key

A client-generated string sent in the Idempotency-Key header on POST requests. mintfax stores the key (keyed by account ID) along with the original response. If the same key appears again within 24 hours, mintfax returns the stored response without re-processing. Prevents duplicate fax submissions from network retries or client-side retry logic. 
curl -X POST https://api.mintfax.com/v1/fax \
  -H "Authorization: Bearer fx_test_abc123def456" \
  -H "Idempotency-Key: 550e8400-e29b-41d4-a716-446655440000" \
  -F "to=+12015550100" \
  -F "file=@document.pdf"
Notes
  • Keys expire after 24 hours.
  • Omitting the header returns X-Idempotency-Key: not provided; recommended as a nudge.
See also

​
MCF / RTN / RTP

Post-page response signals defined by T.30.
  • MCF (Message Confirmation) - the receiver accepted the page.
  • RTN (Retrain Negative) - the receiver detected errors and wants the page resent at a lower speed.
  • RTP (Retrain Positive) - the receiver accepted the page but wants subsequent pages at a lower speed.
These signals drive retry and speed-fallback behavior during a fax session. mintfax exposes T.30 diagnostic codes from the carrier, which include MCF/RTN/RTP outcomes. See also

​
MH / MR / MMR / JBIG

Image compression schemes used in fax, listed here from least to most efficient.
  • MH (Modified Huffman) - one-dimensional, line-by-line encoding. The required baseline for all G3 fax.
  • MR (Modified READ) - two-dimensional encoding that references the previous line. Optional.
  • MMR (Modified Modified READ) - higher-efficiency two-dimensional encoding, typically paired with ECM.
  • JBIG - lossless compression with the best ratios of the four. Less widely supported.
The sending and receiving machines negotiate which scheme to use during the T.30 handshake. See also

​
Multipart fax

A fax with multiple document pages submitted as a single transmission. In the mintfax API, the document is uploaded as one file (PDF, TIFF, or other supported format), and all pages transmit as a single fax session. The pages field on the fax record reflects the total count. See also

​
PHI

Protected Health Information. Any individually identifiable health information transmitted or maintained by a covered entity or business associate, as defined by HIPAA. Fax documents in healthcare workflows frequently contain PHI. When handling PHI through mintfax, operate under a BAA and consider zero-footprint mode. See also

​
Real-time fax

A transmission model where both endpoints maintain a live session for the duration of the call, exchanging T.30 handshake signals, training sequences, and page data synchronously. Compare with store-and-forward, where the API accepts the document and handles delivery in the background. Most carrier-level fax delivery is real-time even when the API layer in front of it is store-and-forward. See also

​
Retry

An automatic re-attempt to deliver a fax after a transient failure (busy signal, no answer, temporary carrier error). mintfax retries based on the configured count (workspace default or per-fax override, maximum 10). The retries_remaining field tracks attempts left. A fax stays in_progress during retries and moves to failed only after all attempts are exhausted. See also

​
Store-and-forward

A delivery model where the sender submits a document to an intermediary (the mintfax API, for example), which queues it and handles carrier delivery in the background. The sender gets back a fax ID and either polls for status or receives a webhook when delivery completes. mintfax is a store-and-forward service: POST /fax returns 201 with status queued, and the fax proceeds from there. See also

​
T.30

The ITU-T recommendation that defines the Group 3 fax protocol. T.30 covers the full session lifecycle: call setup, capability negotiation (DIS/DCS frames), training, page transmission, post-page responses (MCF/RTN/RTP), and session teardown. T.30 diagnostic codes are the most specific source of information about why a fax succeeded or failed. mintfax exposes them via the error_code and error_message fields on fax records. See also

​
T.38

An ITU-T recommendation for real-time fax relay over IP networks. Where G.711 pass-through encodes fax tones as audio, T.38 demodulates the fax signals at the sending gateway, transmits them as structured data packets (IFP), and remodulates them at the receiving gateway. T.38 tolerates packet loss and jitter better than G.711 because the data is structured, not analog audio. See also

​
T.38 pass-through

A network configuration where T.38 fax packets traverse intermediate VoIP infrastructure without being decoded or transcoded. Routers, session border controllers, and switches pass the T.38 data transparently between endpoints. Preserves fax signal integrity across multi-hop IP networks, but every node in the path must support T.38. See also

​
Training sequence

A calibration signal sent before page data during a T.30 fax session. The training sequence lets the receiver synchronize its equalizer and modem to the line conditions. Both sides agree on a modulation speed during negotiation, and the training sequence confirms the line can sustain it. If training fails, the machines fall back to a lower speed (see RTN/RTP). See also

​
Webhook

An HTTP POST request that mintfax sends to your server when an event occurs, such as a fax being delivered or failing. Each payload is signed with HMAC-SHA256 using a per-account signing secret and carries a unique event ID for consumer-side deduplication. Webhooks retry with exponential backoff on failure. Configure endpoints at the workspace level, or override the destination per fax. See also
Last updated: 2026-05-09