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 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.

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