A fax API is a set of REST endpoints that lets your application send and receive faxes programmatically. You make an HTTP request with a document and a phone number, and the provider's infrastructure handles the analog transmission. No fax machine or phone line required. See our [cloud fax guide](/blog/cloud-fax/) for how the underlying technology works.

How do I send a fax with the mFax API?

Create a business API key in the mFax dashboard, then POST a multipart request to https://developers.mfax.to/v1/faxes with an Authorization: Bearer header and two fields — `to` (the recipient in E.164) and `file` (your PDF). mFax returns HTTP 202 with a Fax object you can poll with GET /v1/faxes/{uuid}. Full docs and keys are at developers.mfax.to.

Is a fax API HIPAA compliant?

It can be — if the provider offers TLS 1.2+ encryption, AES-256 at rest, a signed Business Associate Agreement (BAA), and audit logging. Not every fax API qualifies. mFax Business includes a signed BAA and API access from about $9/mo. See our [HIPAA fax API guide](/blog/hipaa-fax-api/) for the full checklist.

Does Twilio still have a fax API?

Twilio fully sunset its Programmable Fax (send and receive) on December 17, 2021. Alternatives like mFax, Telnyx, and Sinch offer complete fax API solutions in 2026, and mFax and Telnyx are common landing spots for ex-Twilio Fax users.

What file format does the mFax API accept?

The mFax send endpoint takes a PDF uploaded as the `file` field in a multipart/form-data request. Many fax APIs also accept DOC/DOCX, TIFF, and image formats and convert them server-side, but for mFax send a PDF.

Fax API: How to Send Faxes Programmatically (2026)

A fax API lets developers send and receive faxes through simple REST calls — no fax machine, no phone line, no protocol knowledge. Learn how the mFax API and other fax APIs work, compare providers and pricing, and integrate faxing into your app.

Frequently Asked Questions

What is a fax API?: A fax API is a set of REST endpoints that lets your application send and receive faxes programmatically. You make an HTTP request with a document and a phone number, and the provider's infrastructure handles the analog transmission. No fax machine or phone line required. See our [cloud fax guide](/blog/cloud-fax/) for how the underlying technology works.
How do I send a fax with the mFax API?: Create a business API key in the mFax dashboard, then POST a multipart request to https://developers.mfax.to/v1/faxes with an Authorization: Bearer header and two fields — `to` (the recipient in E.164) and `file` (your PDF). mFax returns HTTP 202 with a Fax object you can poll with GET /v1/faxes/{uuid}. Full docs and keys are at developers.mfax.to.
Is a fax API HIPAA compliant?: It can be — if the provider offers TLS 1.2+ encryption, AES-256 at rest, a signed Business Associate Agreement (BAA), and audit logging. Not every fax API qualifies. mFax Business includes a signed BAA and API access from about $9/mo. See our [HIPAA fax API guide](/blog/hipaa-fax-api/) for the full checklist.
Does Twilio still have a fax API?: Twilio fully sunset its Programmable Fax (send and receive) on December 17, 2021. Alternatives like mFax, Telnyx, and Sinch offer complete fax API solutions in 2026, and mFax and Telnyx are common landing spots for ex-Twilio Fax users.
What file format does the mFax API accept?: The mFax send endpoint takes a PDF uploaded as the `file` field in a multipart/form-data request. Many fax APIs also accept DOC/DOCX, TIFF, and image formats and convert them server-side, but for mFax send a PDF.