Why T38Fax
The Fax Carrier That Actually Understands Fax
Most SIP providers treat fax as a footnote. T38Fax was built by fax industry veterans who couldn't find a carrier they trusted — so they built one. Here's what that means for your operation.
Built for Fax. Not Adapted for It.
Most companies that offer T.38 are voice carriers who added fax as an afterthought. Their infrastructure was designed for voice calls — predictable, tolerant of modest packet loss, forgiving of timing imprecision. Fax is none of those things. T.38 requires exact timing, clean UDPTL handling, and Error Correction Mode on every call. Voice networks weren’t built for it.
T38Fax was. We’re a company of career fax industry professionals who spent years watching voice carriers fail at fax, and built an alternative. Every technical decision we’ve made since day one has been optimized for one thing: reliable fax transmission at scale.
The four things that actually make the difference are below.
Voice Carriers Aren’t Fax Carriers
Most SIP providers treat T.38 the way they treat every other protocol feature: pass it upstream and hope for the best. Their T.38 “support” means your fax traffic terminates on a carrier they don’t control, whose ECM configuration you’ll never see, and whose routing changes call to call. When something breaks, nobody in the chain owns the stack well enough to diagnose it.
T38Fax exists because we couldn’t find a provider who got this right — so we built one. The full technical picture covers how the stack is architected; this page is about why the architecture matters to your operation.
Consistent T.38
Most SIP providers don't actually run their own T.38 infrastructure, they pass your fax traffic to an upstream carrier whose implementation they don't control and can't fix when it breaks. When you file a support ticket, they escalate to a carrier who escalates to another carrier, and the answer comes back as "try lowering your fax speed."
T38Fax built its own T.38 stack from the ground up. As covered above, gateway placement inside carrier networks is what keeps the whole path under our control. Your equipment talks to our gateways on every call. No upstream handoff. No variable routing that changes call by call. No mystery carrier in the chain whose behavior we can't control.
Read MoreECM Error Correction
Error Correction Mode (ECM) is the part of the fax protocol that detects corrupted pages and requests retransmission. Without it, a page can arrive garbled, or half-blank, or missing its last three lines, with neither the sender nor recipient knowing it happened. The transmission "succeeds." The confirmation page prints. The content is wrong.
Most carriers disable ECM to reduce processing load. It's a quiet decision, invisible to their customers, that makes their fax statistics look fine while your users wonder why critical documents keep arriving unreadable. We insist on ECM for every call. The word "facsimile" means exact copy. That's not optional.
Why It MattersSecurity & Compliance
T38Fax is SOC 2 certified and HIPAA compliant. Because T.38 is a real-time protocol, fax content passes through our network and terminates — we never store it on our servers. This simplifies your compliance posture considerably compared to store-and-forward fax services, where transmitted documents sit in a database that has to be secured, audited, and defended.
For organizations that require encrypted transport, we offer optional IPSec VPN tunnels at no additional charge. Private dedicated circuits and direct cloud connections into AWS and other hosting environments are available for stricter requirements.
Security & Compliance DetailsPremium Support
We don't just support the product, we believe support is the product. Our team consists of fax industry veterans who diagnose issues with protocol traces and T.30 analysis. When you open a ticket, you reach someone who understands the difference between a T.38 negotiation failure, an ECM partial-page retransmission issue, and a misconfigured ATA. You get a real diagnosis, not a suggestion to lower your fax speed and try again.
Unlimited support is included on every plan, free trial through enterprise. We don't gate technical support behind a paid tier. If you're having a problem with your fax configuration, we want to fix it.
Visit the Knowledge BaseWhat Our Customers Say
"We are a VoIP provider with a sizable municipal and government customer base. Trying other carrier's fax over VoIP services proved to be disastrous. For years our policy was POTS ONLY for fax, that is until we discovered T38Fax. After initial testing, we decided to start rolling out to our customers. The support from Stefanie, Morgan, and the whole team has been flawless. I can safely say that they are my favorite carrier to work with!"
— Joseph Sauer, Project Manager, DBO-TSG"T38Fax's customer service and speedy response is second to none. They don't just send you a canned company answer that further confuses you like other companies do. They are super friendly and genuinely want to help."
— Steve Kile, Senior Systems Admin, Yosemite Farm CreditRead more from the organizations that depend on T38Fax every day.
Read All TestimonialsSee the full Power-T.38 product page — architecture details, interoperability certifications, and deployment options.
Our Solution: Power-T.38Frequently Asked Questions
- Most SIP providers don’t run their own T.38 infrastructure. They pass your fax traffic to an upstream carrier whose implementation they don’t control. When something goes wrong, they can’t fix it — because it’s not their system. T38Fax built its own T.38 stack. We place our media gateways inside carrier networks and terminate G.711 audio directly to the PSTN over a single optical hop. Your equipment talks to our gateways on every call. There’s no upstream handoff, no variable routing, and no mystery carrier in the chain whose behavior changes from call to call.
- If it speaks T.38 FoIP, it will work with us. Our Compatibility List covers everything we’ve tested ourselves — fax servers (RightFax, HylaFAX Enterprise, GFI FaxMaker, XMedius), softswitches and IP-PBXs (FreePBX, Asterisk, 3CX, Cisco BroadWorks, FreeSWITCH, NetSapiens), ATA gateways (Grandstream, Cisco SPA, Patton), and a selection of desktop fax machines with native T.38 support. For devices not on the list, our support team is happy to work through the configuration with you — bring us your device and we’ll figure it out.
- Yes. T38Fax is HIPAA compliant and SOC 2 certified. Because T.38 is a real-time protocol, fax content passes through our network and terminates — we never store it on our servers. This simplifies your compliance posture considerably compared to store-and-forward fax services, where documents sit in a database someone has to secure and audit. If your organization requires encrypted transport, we offer optional IPSec VPN tunnels at no additional charge. Private dedicated circuits and direct cloud connections (AWS and others) are available for environments with stricter requirements. A Business Associate Agreement is available on request.
- Security at T38Fax operates at multiple layers. At the network level, we offer IPSec VPN tunnels to encrypt the SIP signaling and media path between your infrastructure and ours. At the compliance level, we are SOC 2 certified and HIPAA compliant — our Security & Compliance page covers our full posture in detail. At the protocol level, the real-time nature of T.38 means we never store fax content — there’s no database of your transmitted documents on our servers. For organizations requiring physical network separation, we can provide dedicated private circuits.
- We offer simple, usage-based pricing with no activation fees, no minimum term, and no volume commitments required to get started. Unlimited number porting is included at no charge. Volume discounts are available for usage above 1,000 minutes per month. Wholesale pricing is available for service providers and resellers who can meet volume thresholds. See our Pricing page for full details, or contact our sales team with questions about your specific volume.
- Sign up for a 30-day free trial. The trial includes full access to the service and unlimited technical support — our team genuinely enjoys a configuration challenge, so bring whatever you’re working with. When the trial ends, the account stops working unless you activate it to a paid plan. There’s no automatic conversion.
T.38 Explained
T.38 Is Key to Faxing Reliably Over the Internet
Not all fax-over-IP services use T.38 — and the ones that don't make it obvious when faxes start failing. This guide explains how T.38 works, why ECM matters, and what to look for in a carrier that takes reliable fax transmission seriously.
Read the Guide