Sinch fax alternative
Sinch supports both sending and receiving faxes, alongside its other communications services. mintfax sends faxes only. If you are comparing them for outbound fax, the main differences include webhook signatures, duplicate request handling, and testing.
Feature comparison
| Feature | Sinch (Phaxio v3) | mintfax |
|---|---|---|
| API style | REST/JSON | REST/JSON |
| Production auth | OAuth 2.0 | Bearer token |
| Environment scoping | Project ID in URL path | Environment inferred from key prefix (mfx_test_, mfx_live_, mfx_acct_) |
| Per-page price | $0.045 flat | $0.060 standard; $0.048 at 100k+/mo; $0.036 at 1M+/mo |
| BAA | Free; signed with DocuSign | Free BAA in the dashboard; separate DPA |
| PHI storage default | Opt-out (storage on unless boxes unchecked in Fax > Services > HIPAA) | Opt-in zero-footprint mode; 30-day content retention default (7-365) |
| Webhook signing | Not supported in v3; HTTP Basic on the webhook | HMAC-SHA256 per Standard Webhooks; per-endpoint whsec_ secret |
| Idempotency on send | Not documented | Idempotency-Key header; 24h expiry; 409 on reuse |
| Send retries | 0-5 per fax | 1-5 per fax; default 3 attempts; backoff 1m / 3m / 5m / 5m |
| Webhook retries | Extended retry window | 3 attempts (10s / 60s / 300s), then stop |
| Error model on send | HTTP status + type discriminator + integer errorCode; HTTP 800 for fetch | 17 API error codes + 10 delivery error codes + optional error_subcode |
| Request tracing | Not documented | X-Request-Id: req_<ULID> on every response; echoed as request_id |
| Sandbox | One test number | Nine test numbers, nine scenarios; same API as live |
| Multi-recipient | Server-side fan-out to N faxes | Single-recipient to field |
| File formats | 7 (.docx, .html, .jpg, .png, .tif, .pdf, .txt) | 8 (PDF, DOCX, XLSX, JPG, PNG, TIFF, HTML, plain text); 10 MB upload |
| Inbound / receive | Yes | No (outbound only) |
| Category | Multiple communications services | Fax-only |
Delivery updates and duplicate requests
Sinch v3 uses HTTP Basic authentication for webhooks; it does not support webhook signatures. mintfax signs each delivery update using HMAC-SHA256 under the Standard Webhooks specification. Your application can verify the signature before using the update.
Sinch’s public fax documentation does not describe an idempotency key. mintfax accepts an Idempotency-Key on send requests and keeps it for 24 hours. Repeating the same request with the same key returns the stored response. Reusing the key with a different body returns an error.
Testing
Sinch documents one test number for simulating a successful outbound fax. mintfax has nine test numbers for outcomes such as successful delivery, busy lines, no answer, and validation errors.
The mintfax sandbox uses the same API as live. Payments and fax deliveries are simulated, and you can use it without buying credits.
Agreements and stored content
Both services offer a BAA you can sign through their dashboards. mintfax also offers a separate DPA. You can download the signed agreements immediately.
mintfax keeps fax content for 30 days by default, configurable between 7 and 365 days. Zero-footprint mode deletes patient information after delivery or failure. See compliance for audit logs and retention details.
Other requirements
Sinch supports inbound fax and other channels, including SMS and voice. mintfax does not receive faxes. If your requirements include a specific certification, check the table and mintfax’s compliance details.
See pricing for mintfax’s rates, or the Sinch migration guide for implementation changes.