Fax Over VoIP in Australia: Why It Fails and What to Do Instead (2026)

When Australian businesses migrate from copper PSTN lines to VoIP on the NBN, fax is one of the first things to break. The failure mode is usually intermittent rather than total: some faxes go through, others fail with a no-answer or mid-transmission error, and the pattern is unpredictable. This drives IT support time and creates reliability problems in industries where fax is still legally or operationally required: healthcare, legal, government suppliers, some financial services, and some manufacturing operations.

The core issue is that traditional fax was designed for the analogue PSTN network. It uses a protocol (V.34 and older variants) that assumes a consistent analogue signal path. VoIP converts audio to digital packets, compresses them, and reassembles them at the other end. A process that introduces slight timing variations (jitter) that are inaudible to the human ear but catastrophic to fax modems.

Why Traditional Fax Fails Over VoIP

Fax machines communicate via analogue modem tones. The fax protocol involves a handshake sequence (capability negotiation), followed by a data transmission phase, followed by a disconnect signal. This handshake is time-sensitive and assumes a consistent audio path with no packet loss, minimal jitter, and no audio compression.

VoIP systems use codec compression (G.711, G.729, Opus) to reduce bandwidth requirements. Even G.711. The highest-quality VoIP codec, the one closest to an uncompressed analogue signal. Introduces enough timing variation to occasionally disrupt fax handshakes. G.729 and other compressed codecs are worse: the compression algorithm removes audio data that is deemed inaudible to humans, which includes exactly the kinds of tones that fax modem negotiation relies on.

Packet loss compounds the problem. Fax error correction (ECM. Error Correction Mode) can compensate for some data errors, but not for packet loss-induced gaps in the audio stream. A 0.5% packet loss rate that is barely noticeable on a voice call can cause frequent fax transmission failures.

The result: a fax machine plugged into the RJ11 port of an NBN-connected ATA (Analogue Telephone Adapter) works sometimes and fails unpredictably. The failure pattern does not correlate obviously with internet speed. It correlates with jitter and packet loss on the network path, which vary throughout the day.

T.38: The Standard Designed to Fix This

T.38 (also called Fax over IP or FoIP) is an ITU standard specifically designed to address the fax-over-VoIP problem. Instead of trying to pass raw fax tones through a VoIP audio stream, T.38 re-encodes the fax data at a higher level. Essentially treating the fax as data rather than audio. And uses a more robust packet transmission method (T.38 uses redundancy to compensate for packet loss in a way that standard RTP does not).

T.38 can work reliably in the right conditions:

• Both the sending and receiving end must support T.38. If your VoIP provider supports T.38 on their end, and the receiving fax machine or system also supports it, the transmission should be significantly more reliable than sending raw fax tones over G.711.
• The network path must have low jitter and packet loss. Even T.38 degrades under poor network conditions, just less catastrophically than analogue-over-VoIP.
• The ATA (analogue telephone adapter) or FXS gateway must support T.38 pass-through. Not all ATAs do.

The problems with T.38 in the Australian market:

• Many Australian VoIP providers and SIP trunk carriers do not support T.38, or support it only on specific plan tiers.
• Many receiving fax machines (especially older models still in use in healthcare and legal environments) do not support T.38.
• Even with T.38 support on both ends, some combinations of VoIP provider, SIP trunk, ATA, and fax machine produce intermittent failures that are difficult to diagnose and resolve.

T.38 is worth trying if both ends support it, but it is not a guarantee of reliable fax operation. The businesses that need truly reliable fax transmission typically use one of the alternative approaches below.

Practical Options for Australian Businesses That Still Need Fax

Option 1: Cloud Fax Service (Recommended for Most)

A cloud fax service replaces your physical fax machine with an internet-based service that receives faxes as PDF email attachments and lets you send faxes from a web portal or email. Popular Australian-accessible cloud fax services include eFax, FaxBetter, DirectFax, and Fax.Plus.

How it works: you get a fax number (can be your existing fax number if it is ported, or a new number). Incoming faxes are received by the service's infrastructure, converted to PDF, and emailed to you. Outgoing faxes are sent via email (attach a PDF, address it to [faxnumber]@fax-service.com) or via a web portal. The physical fax machine is retired.

Advantages:

• Completely reliable. Fax transmission happens on dedicated fax infrastructure, not over your NBN connection
• No physical machine to maintain, jam, or run out of paper
• Faxes arrive as searchable PDFs rather than thermal paper curls
• Send and receive from anywhere. Works from a mobile phone
• Monthly cost: typically $15 to $40/month for a small business volume plan

Considerations:

• You need to port your existing fax number to the cloud fax service. This requires your number to be portable (geographic numbers are portable; some integrated fax-only numbers may be more complex)
• Staff who are accustomed to printing a document and faxing it physically need to learn a new workflow (upload PDF to a web portal or email it)
• Some regulated industries have specific requirements about electronic records. Confirm a PDF fax record satisfies your obligations before retiring the physical machine

Option 2: Keep One Copper Line Specifically for Fax

If you need to continue using a physical fax machine, the most reliable approach in Australia is to keep a single copper PSTN line exclusively for the fax machine while migrating all voice calls to VoIP. This is a hybrid approach that is more common than it might sound. Many medical practices, law firms, and government suppliers operate this way.

The copper line is completely independent of your NBN connection. Fax transmissions over copper are as reliable in 2026 as they were in 1995. The trade-off is the ongoing cost of the copper line: approximately $25 to $40/month for a basic PSTN line plus call costs.

Important timing consideration: Telstra is progressively retiring the copper PSTN network as NBN rollout progresses. In areas where NBN has been fully activated, copper PSTN services are eventually being disconnected. Check whether copper PSTN lines are still available at your address and for how long. In many CBDs and urban areas, the PSTN retirement timeline is known; in others it is still being determined. If you are in an area where copper is being retired, the cloud fax option becomes a more immediate necessity.

For context on the copper shutdown timeline, see our guide to the PSTN shutdown in Australia.

Option 3: Dedicated Fax ATA with T.38

An ATA (Analogue Telephone Adapter) converts an analogue fax machine signal to a digital SIP connection. Using a dedicated, high-quality fax ATA. Rather than the built-in ATA on an NBN modem. With T.38 support can significantly improve fax reliability over VoIP.

Recommended hardware: Cisco SPA112, Grandstream HT801/HT802, or Patton ATAs designed specifically for fax. These devices support T.38 fax relay natively and include jitter buffers optimised for fax rather than voice. They are configured with dedicated SIP credentials from your VoIP provider's T.38-capable fax line.

This approach is more reliable than plugging a fax machine into the NBN modem's phone port, but it requires: your VoIP provider to offer T.38 fax SIP lines (not all do), the receiving fax machines to support T.38, and some technical configuration to get the ATA settings right. Expect to spend 2 to 4 hours on initial configuration and testing.

Option 4: FXS Gateway for Larger Fax Volumes

Businesses that send or receive large volumes of faxes (healthcare with multi-line fax operations, large legal practices, government agencies with bulk document workflows) may benefit from an FXS gateway: a device that connects multiple analogue fax machines to a SIP trunk, with T.38 support at a hardware level that exceeds what a single ATA provides.

Grandstream TA800 and Sangoma Vega gateways are examples used in Australian enterprise deployments. This is a more complex and expensive configuration (hardware cost $300 to $2,000+ depending on port count) and is only worth considering for businesses with genuine high-volume fax requirements that cannot be met by cloud fax services.

Fax Requirements by Industry: What Australian Regulations Actually Require

Many Australian businesses continue using fax out of habit or vague compliance concern rather than a specific legal requirement. Before investing in a fax continuation strategy, it is worth checking whether fax is actually required:

Healthcare: The My Health Record system and e-referral platforms (HealthLink, Argus) have dramatically reduced the genuine need for fax in many healthcare contexts. Most pathology requests, referrals, and clinical communications can now be transmitted digitally through compliant channels. However, some older healthcare systems and some specialists still operate primarily via fax. Australian RACGP guidelines do not mandate fax; they mandate secure communication of clinical information. A compliant cloud fax service that encrypts documents in transit and provides audit trails typically satisfies this requirement.

Legal: Courts, tribunals, and government agencies in Australia have progressively moved to email and online filing systems. Physical fax for court filings is largely obsolete in most jurisdictions. Check the specific requirements of courts or agencies you file with. Most now have documented procedures for email and electronic lodgement that supersede fax.

Government suppliers: Procurement and invoicing processes have largely moved to electronic document management systems. If a government agency is requiring fax for procurement communications, this is unusual and worth querying directly. They may have an electronic submission alternative that is not well-publicised.

Financial services: ASIC and APRA-regulated entities have their own record-keeping requirements. A cloud fax service that provides a PDF record of all sent and received faxes with timestamps typically satisfies document retention requirements. Confirm with your compliance team.

Comparison: Fax Options for Australian Businesses

How to Migrate to Cloud Fax Without Losing Your Number

Porting your fax number to a cloud fax service follows the same process as porting any other phone number. The fax number is a geographic DID (direct inward dial) number and is portable under ACMA's number portability rules.

Steps:

1. Sign up with a cloud fax service and confirm they accept ported Australian numbers. Most do, but confirm before starting the process.
2. Initiate the port through the cloud fax service's portal. They will ask for your account details with your current provider and the number to be ported.
3. Allow 3 to 10 business days for a geographic fax number port. During porting, your existing fax machine still receives faxes on the old service until the port completes.
4. Test the cloud fax service with a new test number first (before porting your main number) to confirm delivery and PDF quality meets your requirements.
5. Once porting is complete, communicate the new workflow to staff and retire the physical fax machine.

For the full porting process, see our guide to number porting in Australia.

What Most Businesses Get Wrong

Assuming the problem is the VoIP provider's fault. Fax failure over VoIP is usually a protocol incompatibility issue, not a provider quality issue. Switching VoIP providers to fix fax reliability rarely works unless the new provider specifically offers T.38 support and the old one did not. Diagnose the issue correctly before switching providers.

Spending months trying to make a physical fax machine work on VoIP. The time spent configuring ATAs, testing codecs, adjusting jitter buffers, and troubleshooting intermittent failures is almost always worth more than the cost of a cloud fax service for the lifetime of the business. Cloud fax is the correct solution for most Australian businesses with low-medium fax volume. The physical fax machine is the wrong starting assumption.

Not checking whether fax is actually legally required. Some businesses maintain a fax machine because they have always had one, not because any regulatory requirement mandates it. Before investing in a fax continuation strategy, confirm whether any of your actual compliance obligations specifically require fax transmission rather than secure electronic document delivery.

Your Next Steps

If you are migrating from a copper PSTN line to VoIP and have a fax machine:

1. Assess whether your fax volume justifies the complexity of a physical fax continuation strategy. Under 20 faxes per month is almost certainly better served by cloud fax.
2. Check whether any of your senders or receivers will also move to cloud fax. If your major correspondent is also migrating, the fax problem may resolve itself.
3. If you are keeping a fax machine, check whether your VoIP provider supports T.38 and whether your fax machine supports T.38 receive. Test it before committing to this approach.
4. If you are moving to cloud fax, select a service, test with a new number, then port your existing fax number.
5. Communicate the workflow change to staff early. Sending a fax by email takes 2 minutes to learn but requires advance notice.

For more on what to expect when migrating from copper to VoIP, see our full migration guide for Australian businesses.