Organizations still running the ancient IIS 6.0 SMTP virtual server face a hard deadline. With Windows Server 2025 removing the component entirely and mainstream support for older servers long past, IT teams must find a replacement for basic mail relay. Microsoft’s official guidance points to the Exchange Edge Transport role. But swapping a free, lightweight SMTP relay for a full Exchange server introduces a licensing nightmare that many admins are only now confronting.

In dozens of recent forum threads, system administrators share the same rude awakening. They download Exchange Server, install the Edge Transport role, configure it for anonymous SMTP relay from printers, applications, and monitoring systems, and then start wondering: do we need Client Access Licenses? The short answer is yes—with nuances that can multiply costs dramatically.

The Vanishing of IIS 6.0 SMTP

Microsoft originally bundled the SMTP service from IIS 6.0 with Windows Server 2003, and it lived on as a feature in subsequent versions through Windows Server 2012 R2, albeit disconnected from the IIS stack. In Windows Server 2016, the SMTP Server feature was removed from the GUI but could be added via PowerShell. By Windows Server 2022, it was deprecated and no longer installable. The final blow came with Windows Server 2025, where the binaries are absent altogether. For any shop still depending on this relic, the clock has run out.

The functionality was simple: accept anonymous SMTP messages from internal devices and forward them to a smart host or directly to external recipients. No authentication, no user mailboxes, no complex configuration. It cost nothing beyond the Windows Server license.

The Official Escape Route: Exchange Edge Transport

Since the removal of the built-in SMTP relay, Microsoft’s recommended path is to deploy an Exchange Server with the Edge Transport role. Edge Transport is designed to sit in the perimeter and handle all external mail flow—antispam, antivirus, routing. It can also function as a pure SMTP relay with minimal configuration. The role does not require Active Directory, stores no user data, and can be set up on a domain-joined or workgroup machine.

Deployment is straightforward. Download the latest Exchange Server ISO (the current supported path in 2026 is Exchange Server Subscription Edition, with Exchange Server 2019 still in extended support), run the installer, and select the Edge Transport role. Post-installation, you configure a send connector, set up allowed relay domains, and enable anonymous relay on the Receive connector. Done.

Except that's where the licensing questions begin.

The Unspoken Cost: Exchange Licensing and CALs

Here is the core of the confusion—and the reason so many admins are upset on forums. Exchange Server is not free. Every instance, even Edge Transport, requires a server license. But the bigger sting is the Client Access License (CAL) requirement.

Microsoft’s licensing model for Exchange states that any person or device that accesses the server software requires a CAL. “Access” includes sending email. Does a multi-function printer scanning to email count as a device accessing the Exchange Edge Transport server? Yes. Does a batch job that generates invoices and fires them off via SMTP count as a device? It depends on whether it’s considered a “user” or “device”—but in practice, Microsoft’s licensing has long held that any entity that sends mail through an Exchange server needs a CAL, unless it falls under a few narrow exceptions.

An official Microsoft licensing document clarifies: “If a user or device directly or indirectly accesses Exchange Server—for example, through a multifunction device that forwards scanned documents to email—a CAL is required.” There is no generic “SMTP relay” exemption for Edge Transport. The server role is licensed as part of Exchange, not as a standalone gateway product.

The Math: Costs Spiral Quickly

Consider a 500-user organization with 200 printers, scanners, and IoT devices that send automated emails. Under the IIS 6.0 SMTP model, none of these required extra licensing. Moving to Exchange Edge Transport, each device that sends mail now technically needs a Device CAL. At an approximate cost of $90 per Device CAL (pricing for Exchange Server Subscription Edition in 2026, subject to changes), that’s $18,000 for the 200 devices. Plus the server license for Exchange, which for Edge Transport requires either a standard Exchange Server license or, in some scenarios, a specific Edge Transport license. In practice, many organizations buy a full Exchange Server license and position it as a standalone server.

But it gets more complex. If those printers also relay mail through authenticated user accounts (for audit trails), then each user who authenticates needs a User CAL. That could double the licensing burden.

Forum discussions reveal that many admins never considered CALs because they viewed Edge Transport simply as a “replacement for IIS SMTP” and assumed the same licensing model applied. A senior community member summarized it bluntly: “Microsoft has never offered a free SMTP relay after IIS 6.0. The minute you touch Exchange, you’re on the hook for CALs.”

Nuances and Possible Exceptions

A few caveats come into play. The Exchange Server 2019 documentation previously hinted that the Edge Transport role could be licensed separately under certain programs, but that option has been progressively removed. By 2026, the standard licensing model for Exchange SE is the only one available.

Another nuance is the “External Connector License.” This is designed for external users accessing Exchange, but it may also cover scenarios where your relay sends to external recipients on behalf of internal devices. The External Connector is licensed per server, not per user, which could be more economical if you have thousands of devices but only a single Edge server. However, it’s only available under Volume Licensing or Enterprise Agreements and requires a conversation with a licensing specialist.

A final gray area: if the Edge Transport server simply forwards mail from anonymous internal sources to an External Smart Host (such as Microsoft 365 or a third-party filtering service), does each internal device “benefit” from the Exchange server? According to the strict wording of the Product Terms, yes, because the device is “directly or indirectly accessing” the software. Microsoft has not published a clear exemption for anonymous relay-only usage.

Community Workarounds and Third-Party Alternatives

The licensing shock has driven many to seek alternatives. In forums, three strategies dominate:

  1. Stay on Windows Server 2012 R2 as long as possible. Some admins with extended security updates patches intend to keep IIS 6.0 SMTP running until the hardware dies. This is not a long-term solution and poses security risks.

  2. Use a third-party SMTP relay. Software like hMailServer, Postfix on a Linux VM, or commercial products like MailEnable or SMTP2Go can replicate IIS SMTP functionality without Exchange CALs. The recurring theme: “Free SMTP relay on Windows is dead, but Linux gives you the same for nothing.” Many organizations are now building small Linux VMs just for SMTP relay, side-stepping Microsoft licensing entirely.

  3. Leverage Microsoft 365’s SMTP relay capabilities. Microsoft 365 can be configured to relay mail from on-premises devices (Option 2: Direct Send). This requires a static IP, a connector in Exchange Online, and suitable DNS records. For some, it eliminates the need for an on-prem relay altogether. But it still requires each sender to authenticate or be IP-whitelisted, and volume limits apply.

These workarounds underscore a growing dissatisfaction: many long-time Windows admins feel that Microsoft has removed a basic networking utility and pushed them toward a costly licensed product without a clear bridge.

What Microsoft Says (and Doesn’t Say)

Microsoft’s official documentation for “SMTP relay in Exchange Server” focuses on configuration, not licensing. The Product Terms are the authoritative source. There, the requirement is unequivocal: “Exchange Server 2019 and later require a Server License for each instance and a Client Access License for each user or device that accesses the server software.” The term “accesses” is not defined in a way that exempts simple SMTP relay.

A 2025 licensing brief from a large Microsoft reseller attempted to address the question: “Edge Transport role deployed solely for SMTP relay: CALs required for all senders. External Connector License may be an alternative if senders are not employees or affiliates.” However, even the External Connector has a minimum purchase of 25 and is often more expensive than expected.

Microsoft has not announced any plans to introduce a lightweight, licensed SMTP server for Windows Server. The message is clear: if you need a supported SMTP relay on Windows, you’ll need to pay for Exchange or consider alternative platforms.

Real-World Impact: A Case Study

A mid-sized manufacturing firm with 800 employees and 450 shop floor devices (scanners, label printers, legacy monitoring systems) recently completed their IIS to Edge Transport migration. They deployed two Edge Transport servers for high availability. After an audit, they realized they needed 1,250 Device CALs (800 users plus 450 devices). The cost exceeded $100,000 for the first year alone, far outstripping the $3,000 they paid for a Windows Server License and third-party SMTP software the previous year. The IT director told the community: “We were blindsided. Nobody at Microsoft or our reseller told us about the CALs until after we deployed. Now we’re scrambling to rip out Edge Transport and put in Postfix.”

Cases like this are fueling a vigorous debate about whether Microsoft is exploiting a necessary migration to push Exchange licensing. Some suspect the motive is to accelerate cloud adoption by making on-premises alternatives less attractive.

The Path Forward

For organizations that cannot stomach the Exchange licensing, the clear recommendation is to avoid Edge Transport for pure SMTP relay. Instead, opt for a third-party SMTP server on Windows (though free Windows options are scarce and often unmaintained) or deploy a Linux-based relay. The learning curve for a simple Postfix configuration is a week or two, and the license cost is zero.

Those committed to the Microsoft stack should engage licensing specialists to explore the External Connector option and negotiate Volume Licensing terms. A few have reported success obtaining a “No-CAL bundle” for Edge Transport under certain enterprise agreements, but this is anecdotal and not publicly documented.

In the long term, the industry will likely see a proliferation of tiny Linux VMs handling SMTP relay, while Exchange Edge Transport remains the domain of organizations that already have Exchange CALs universally assigned. The era of the free, built-in Windows SMTP relay is over, and the replacement landscape is messy, expensive, and poorly communicated.