From the text I'm not sure the idea really is to make the author money. If anything, presumably any code others contribute now will be copyleft, meaning if the patches are integrated and re-distributed by the author he can charge for distribution - but have to distribute under copyleft.

I also wonder how many corporations integrate and redistribute nodemailer; I'm sure there's a few - but I'm guessing most just use nodemailer. Apart from paranoid legal teams, the licence change shouldn't make any difference.

Now, someone distributing a firewall appliance using nodemailer for sending email alerts would have to provide customers with a copy of nodemailer source under copyleft - along with any changes. I still don't see why that would translate to payments to the author.

It does. For example MongoDB is AGPL. BUT if you add nodemailer to your project as a dependency and you link to it GPL will stick. This is why MongoDB's drivers are Apache license but the database itself is AGPL.

So, someone told me that your code need not be GPL but that the combination of your code + a gpled program must be.

IANAL, but this sounded reasonable to me.

The trick is in what constitutes "combination", particularly re. static vs. dynamic linking.

My understanding is that, at least with LGPL, you can have a closed source program distributed with a LGPL shared object/dll (plus license text) that gets loaded dynamically, but I don't think you can do that with GPL proper.

Static linking (IIUC) is right out (for closed source projects).

Not sure if it makes a difference in this case either, however the method is being used successfully by projects like x264, x265, which distribute under GPL, but also offer commercial licenses allowing them to be incorporated into proprietary solutions.

What if you do an on-prem SAS deployment? Think that counts.