Fax Server Software: How It Works and How to Choose

A fax server is software that sends and receives faxes over the internet instead of a physical fax machine and phone line. It turns email, a web browser, or an application into a fax endpoint, routes the document through a SIP trunk using the T.38 protocol, and delivers it to any traditional or digital fax number. One server can replace a whole room of fax machines.

If your team still walks paper to a beige box in the corner, you are paying for hardware, toner, dedicated lines, and lost documents. Fax server software removes all of that. It also gives you something a fax machine never could: encryption, audit trails, multi-user accounts, and the option to run the whole thing under your own brand. This guide explains what fax server software is, how it works, the deployment options, and how to pick the right one.

What is fax server software?

Fax server software is an application that handles fax transmission digitally. Users submit a document from email or a web portal, the server converts it to a fax image, and it carries the call over IP rather than an analog line. Incoming faxes arrive the same way and land in an inbox or a folder instead of a paper tray. Below are the terms you will meet again and again.

FoIP (Fax over IP)

Sending fax signals across an IP network rather than the traditional public telephone line. This is the foundation every fax server is built on.

T.38

The protocol that carries a real-time fax call over IP. It packages the fax tones so they survive the trip across the internet without the dropouts that plague plain voice codecs.

SIP trunk

The virtual phone line that connects your fax server to the outside telephone network. It replaces the copper line that used to plug into the back of a fax machine.

Email-to-fax and fax-to-email

Send a fax by emailing it as an attachment, and receive faxes as files delivered straight to an email address. No client software needed.

Multi-tenant

A single installation that hosts many separate organizations, each with its own users, numbers, and isolated data.

White-label

The ability to brand the portal, emails, and interface as your own product, so you can resell the service under your company name.

How a fax server works

The flow is simpler than the acronyms suggest. A user submits a document, the server renders it into a fax image, and a media engine places the call over a SIP trunk. ICTFax uses FreeSWITCH as that media engine, which handles the T.38 negotiation and the call itself. Figure 1 shows the path of an outbound fax and the matching inbound route.

Because the call runs over IP, the document is just data until the moment it reaches a legacy fax machine. That is what makes encryption, retention rules, and detailed logs possible, none of which a standalone fax machine can offer.

Deployment options: self-hosted, hosted, and white-label

Not every fax server is sold the same way. The three common models suit very different buyers.

Self-hosted open source

You install the software on your own server and keep full control of the data and the source code. ICTFax has an open source community edition for exactly this. It fits IT teams that want to own their stack and customize it.

Hosted (cloud)

A provider runs the server for you and you log in to a portal. Less control, faster to start, and no machine to maintain.

White-label service provider edition

A multi-tenant build that lets you resell hosted fax to your own customers under your brand. ICTFax SP Edition is built for this, with branded portals, emails, and per-tenant isolation.

Multi-tenant and white-label architecture

The service provider edition is where fax server software earns its keep for telecom resellers and managed service providers. One installation hosts many clients. Each client gets isolated users, numbers, and data, while you control the trunks and resources from the top. Figure 2 shows how the roles stack.

ICTFax SP Edition assigns three clear roles. The admin owns the setup, configures trunks and routes, creates tenants, and allocates resources such as DIDs and dedicated trunks. The tenant or client manages its own users, distributes its fax quota, and applies its own branding. The user sends and receives faxes, runs fax campaigns, and manages contacts. Because every tenant is isolated, one client never sees another client’s data.

Key features to expect from fax server software

Security and HIPAA compliance

Faxes often carry medical records, contracts, and other sensitive data, so security is not optional. ICTFax encrypts incoming fax documents the moment they arrive and stores them in encrypted form. Even an administrator cannot read them. Only the destination user, holding the encryption key, can decrypt and download a fax. Retention rules then delete documents automatically after a set period. If compliance is your main concern, read our deeper guide to HIPAA compliant fax server software.

Email-to-fax, web faxing, and campaigns

Users send a fax by emailing an attachment or by uploading through a web portal. Incoming faxes are delivered to email as files. For high-volume needs, fax campaigns send the same document to many numbers at once. If most of your faxing starts in a browser, our note on web-to-fax server software covers that workflow in detail.

Trunk and route management

The admin configures SIP trunks and routing rules, and can assign a dedicated trunk to a specific tenant when a client needs guaranteed capacity. See dedicated trunk support for how that is set up per client.

Fax server software vs a traditional fax machine

How to choose the right fax server

Match the software to how you actually work. Run through this checklist before you commit.

• Decide on deployment: self-hosted for control, hosted for speed, white-label if you plan to resell.
• Confirm real T.38 support so transmissions stay reliable over IP.
• Check security depth: encryption at rest, access keys, and automatic retention if you handle protected data.
• Look for email-to-fax and web faxing so staff need no special client.
• For providers, require true multi-tenant isolation and per-tenant branding.
• Prefer open source if you want to audit or customize the source code.
• Verify trunk flexibility, including dedicated trunks for high-volume clients.

Frequently asked questions