Can you fax over VoIP?

Technically yes, but it is unreliable. VoIP compresses audio in ways that distort fax tones, causing frequent failures. You can improve success rates by using the G.711 codec and T.38 protocol, but cloud fax services like [mFax](https://mfax.to) are far more reliable.

Why does my fax machine not work on my VoIP phone line?

Fax machines send analog tones designed for the traditional phone network. VoIP digitizes and compresses those tones into packets, which introduces jitter, packet loss, and latency — all of which corrupt the fax signal. Even 1–2% packet loss can cause a fax to fail completely.

What is the T.38 protocol and does it fix VoIP fax issues?

T.38 is a protocol designed specifically for fax over IP networks. It converts fax tones into data packets in a fax-aware way, reducing errors. It helps but requires support from both your VoIP provider and the receiving end, which is not always available.

Is cloud fax more reliable than VoIP fax?

Yes. Cloud fax services like [mFax](https://mfax.to) bypass VoIP entirely by connecting directly to the phone network via dedicated fax infrastructure. This eliminates jitter, codec, and packet loss issues — delivering a 98% success rate.

What VoIP codec should I use for faxing?

Use G.711 (also called G.711u or PCMU). It is an uncompressed codec that preserves the analog fax tones. Avoid G.729 and other compressed codecs — they strip out frequencies that fax machines need.

VoIP Fax Problems: Why Fax Fails on VoIP & How to Fix It

VoIP fax problems are caused by packet loss, codec compression, and jitter. Learn why fax fails on VoIP and 6 proven fixes to get it working — or switch to a more reliable method.

Frequently Asked Questions

Can you fax over VoIP?: Technically yes, but it is unreliable. VoIP compresses audio in ways that distort fax tones, causing frequent failures. You can improve success rates by using the G.711 codec and T.38 protocol, but cloud fax services like [mFax](https://mfax.to) are far more reliable.
Why does my fax machine not work on my VoIP phone line?: Fax machines send analog tones designed for the traditional phone network. VoIP digitizes and compresses those tones into packets, which introduces jitter, packet loss, and latency — all of which corrupt the fax signal. Even 1–2% packet loss can cause a fax to fail completely.
What is the T.38 protocol and does it fix VoIP fax issues?: T.38 is a protocol designed specifically for fax over IP networks. It converts fax tones into data packets in a fax-aware way, reducing errors. It helps but requires support from both your VoIP provider and the receiving end, which is not always available.
Is cloud fax more reliable than VoIP fax?: Yes. Cloud fax services like [mFax](https://mfax.to) bypass VoIP entirely by connecting directly to the phone network via dedicated fax infrastructure. This eliminates jitter, codec, and packet loss issues — delivering a 98% success rate.
What VoIP codec should I use for faxing?: Use G.711 (also called G.711u or PCMU). It is an uncompressed codec that preserves the analog fax tones. Avoid G.729 and other compressed codecs — they strip out frequencies that fax machines need.