---
title: T.38 ECM Test — Verify Your Fax Over IP Error Correction Mode | T38Fax
description: Test your fax line for T.38 ECM support — free. T38Fax's self-test checks whether your SIP infrastructure passes error-corrected fax traffic correctly.
---

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# Does Your T.38 Carrier Support ECM?

### Run our automated ECM test. Results by email in minutes.

[Error Correction Mode (ECM)](https://helpdesk.t38fax.com/hc/en-us/articles/360052595692-What-is-ECM-and-why-do-I-need-it) is the mechanism that makes fax transmission reliable. When two fax machines exchange a document using the [T.30 fax protocol](https://helpdesk.t38fax.com/hc/en-us/articles/360053046371-T-30), ECM compares data at the end of each page and retransmits anything that arrived corrupted or incomplete. Without it, every page is a single attempt — what the receiver gets is what they get, noise included. For fax servers handling regulated documents, that's not a gap you can afford.

> Over 90% of T.38 calls proceed without ECM. [Most carriers disable it to reduce processing overhead.](https://blog.t38fax.com/blog/ecm-t38-dirty-little-secret) If you're running a fax server over a SIP trunk, there's a good chance yours has too — and you may not know it.

The ECM Challenge is our automated test facility. Submit your fax number and we'll check your inbound and outbound ECM status in minutes, at no charge.

1. Submit the form with your work email and fax number.
2. We send you a test fax and email you whether ECM was active on the inbound call.
3. Fax the document back to us. We check your outbound ECM status and email you the result.

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### Take the ECM Challenge!

#### About

  T38Fax.com is a T.38 Fax over IP (FoIP) service provider. We offer PSTN termination and origination (fax sending and receiving) over SIP trunks that have been optimized to offer extremely reliable faxing over WAN and LAN connections . Take advantage of our 30-day free trial, connect any T.38-capable device to our network and experience reliable fax send & receive with no wires, and no strings attached!

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