Oh, government email domain would scare anyone off. It's as bad as a "fbi.com" address. I doubt the permission is really there as the post says, what I have seen is the contrary. Anyway, try with a regular email address. If you want, as background story, say you're a student in a third-world country. That's how I lived before Sci-Hub (via VPN) and it worked out most of the time (e.g. ~75% success rate).

Professors these days are extremely overworked - it's possible it simply got lost, plus it's not their business to provide a copy, especially for someone they think might be able to get one via their own means. Anyway you are right: it doesn't always work.:-)

Try contacting the non-lead authors (even if the article says "contact email"; usually the journal insists you pick one, but the others are also free to send you the article.)

When I was in academia, my inbox was like 40% emails like "publish your next article here", " you are invited to conference x", "your article on x". You get a lot of spam that is generated with text snippets from your work, so it is very targeted. You just have to start ignoring most emails. The other 60% is just work convos from known sources, so it is very easy to separate the two. Or kind of... you could still get an invitation or a review request, but you sort of know peoples names and names of joirnals. I guess its just hard to get by this.

I've not tried much, but it has worked for me from a normal Gmail address.

I graduated 4 years ago and don't have access to my academic email anymore. So maybe checking for an author still at the institution might help. Could also be unlucky.