Where should the offer of modified source required by the AGPL be included?

[DemiMarie]

If a user uses a modified version, where should they include the offer of source required by the AGPL? It’s easy to include it in the web UI, but other protocols have no reasonable way (that I know of) to provide the offer in a place the end-user will see it. (The SMTP greeting is not typically end-user visible.)

The best solution I can think of is to have a single URL that is automatically included everywhere it needs to be, and for Stalwart Labs to specify that this is sufficient. Those building modified versions would then only need to change this URL.

Disclaimer: I am not a lawyer.

[mdecimus]

Under the AGPLv3, users of the software must provide access to the modified source code if they run a modified version over a network. The license specifies that this access should be provided in a way that is "prominent" and "appropriate," but it does not strictly mandate how this is done, leaving some flexibility.

For protocols where direct interaction with end-users is limited or non-existent (e.g., SMTP), providing the source offer through the web UI (if available) is indeed a common and practical approach. This ensures the offer is visible to anyone who interacts with the service in a meaningful way.

Your idea of a standardized URL (e.g., pointing to a hosted page or repository containing the source code) that can be reused in multiple contexts is a possible solution.

I’m also not a lawyer, so this suggestion is provided as a community perspective rather than formal legal advice. For complex licensing questions, I recommend consulting a legal professional.

[DemiMarie]

I still think it would be a good idea for Stalwart to provide an official statement in its documentation, for two reasons:

1. Consulting a lawyer is very expensive.
2. Stalwart Labs is the copyright holder for Stalwart Mail, so it can state what it requires.