What is the difference between FoIP and VoIP?

VoIP (Voice over IP) carries voice calls over IP networks. FoIP (Fax over IP) carries fax transmissions over the same networks — but fax is far less tolerant of packet loss, jitter, and compression. FoIP requires specialized protocols like T.38 or store-and-forward to work reliably, while VoIP works fine with standard voice codecs.

Can you fax over a VoIP line?

Yes, but it is unreliable without proper configuration. Standard VoIP compresses audio in ways that destroy fax tones. You need the G.711 codec at minimum, and ideally the [T.38 protocol](/blog/t38-fax-protocol/) for acceptable success rates. Cloud fax services like [mFax](https://mfax.to) bypass VoIP entirely and are far more reliable.

Is fax over IP reliable?

It depends on the method. G.711 passthrough achieves roughly 80% success rates. T.38 fax relay reaches 85–92%. Cloud fax (store-and-forward) exceeds 96%. Traditional analog fax over PSTN achieves about 95%. For mission-critical faxing, cloud fax is the most reliable IP-based option.

Is fax over IP HIPAA compliant?

It can be, but you need encryption (TLS/SRTP), a Business Associate Agreement (BAA) with your provider, and audit logging. Real-time T.38 transmissions may qualify for the HIPAA "conduit exception," but store-and-forward cloud fax with [end-to-end encryption](/blog/fax-encryption/) is the safer choice for PHI.

What is the best fax over IP method?

For most businesses, cloud fax (store-and-forward) is the best method. It avoids the real-time packet loss problems that plague T.38 and G.711, delivers 96%+ success rates, and requires zero hardware or VoIP configuration. Services like [mFax](https://mfax.to) handle the entire transmission layer.

Fax over IP (FoIP): How It Works & Best Practices

Fax over IP (FoIP) sends fax documents across internet networks instead of phone lines. Learn how FoIP works, the three transmission methods, deployment options, and best practices for reliable IP fax — plus when cloud fax is the smarter choice.

Frequently Asked Questions

What is the difference between FoIP and VoIP?: VoIP (Voice over IP) carries voice calls over IP networks. FoIP (Fax over IP) carries fax transmissions over the same networks — but fax is far less tolerant of packet loss, jitter, and compression. FoIP requires specialized protocols like T.38 or store-and-forward to work reliably, while VoIP works fine with standard voice codecs.
Can you fax over a VoIP line?: Yes, but it is unreliable without proper configuration. Standard VoIP compresses audio in ways that destroy fax tones. You need the G.711 codec at minimum, and ideally the [T.38 protocol](/blog/t38-fax-protocol/) for acceptable success rates. Cloud fax services like [mFax](https://mfax.to) bypass VoIP entirely and are far more reliable.
Is fax over IP reliable?: It depends on the method. G.711 passthrough achieves roughly 80% success rates. T.38 fax relay reaches 85–92%. Cloud fax (store-and-forward) exceeds 96%. Traditional analog fax over PSTN achieves about 95%. For mission-critical faxing, cloud fax is the most reliable IP-based option.
Is fax over IP HIPAA compliant?: It can be, but you need encryption (TLS/SRTP), a Business Associate Agreement (BAA) with your provider, and audit logging. Real-time T.38 transmissions may qualify for the HIPAA "conduit exception," but store-and-forward cloud fax with [end-to-end encryption](/blog/fax-encryption/) is the safer choice for PHI.
What is the best fax over IP method?: For most businesses, cloud fax (store-and-forward) is the best method. It avoids the real-time packet loss problems that plague T.38 and G.711, delivers 96%+ success rates, and requires zero hardware or VoIP configuration. Services like [mFax](https://mfax.to) handle the entire transmission layer.