How exactly would it be viral in this case? I ask because it's damned confusing. Since this would be an email server, wouldn't it be a drop-in component in most folks' infrastructure? If I understand it correctly, it would just require me to make the source code of the email server/client itself available to my users...not any of my other unrelated infrastructure apps, correct?
This is the problem with the GPL/AGPL- what exactly must be open sourced under what conditions has been debated many times, and different people/groups have come to very different conclusions.
The "Corresponding Source" for a work in object code form means all the source code needed to generate, install, and (for an executable work) run the object code and to modify the work, including scripts to control those activities. However, it does not include the work's System Libraries, or general-purpose tools or generally available free programs which are used unmodified in performing those activities but which are not part of the work.
Please point out what exactly the different conclusions are to that text.
I am not an expert on the various points of the debate- I only know it exists. You can Duck Duck Go for "gpl derivative work definition" and find some references to this debate. Perhaps someone else has a specific answer for your question, sorry.
The AGPL is exactly the same as the GPL, except that if there is a button to click to download the source code of the program, you are not allowed to remove that button.
If the Program as you received it is intended to interact with users through a computer network and if, in the version you received, any user interacting with the Program was given the opportunity to request transmission to that user of the Program's complete source code, you must not remove that facility from your modified version of the Program or work based on the Program, and must offer an equivalent opportunity for all users interacting with your Program through a computer network to request immediate transmission by HTTP of the complete source code of your modified version or other derivative work."
That last part--"derivative work"--is somewhat the rub.
If that part of the informal FAQ worries you that it might be interpreted in some strange way, just look at the actually license and read it.
Notwithstanding any other provision of this License, if you modify the Program, your modified version must prominently offer all users interacting with it remotely through a computer network (if your version supports such interaction) an opportunity to receive the Corresponding Source of your version
The definition of Corresponding Source code is listed earlier in this HN thread.
