If you are using Laravel's mail driver you shouldn't have to add any additional headers etc. I don't know what your technical knowledge level is, but email is rather complicated and if you are getting put into spam it could be for a variety of DNS reasons--not just the headers. What email service are you using and what do the DNS settings look like?

I'm using my hosting providers' SMTP service, the name is Fastnom and the DNS set for SMTP is 178.249.187.215
Emails sent to hotmail.it are correctly received into the inbox.

More specifically, I was referring to DNS settings like SPF and Reverse DNS which are factors that determine whether something is spam or not:

http://mxtoolbox.com/spf.aspx https://mxtoolbox.com/problem/smtp/smtp-reverse-dns-resolution

I am not an expert in this matter, but here are couple of things you might want to do first.

To determine why it is considered as spam, you should really take a look at the email source code. Check Received-SPF for its status (pass, fail, softfail, neutral, etc.) and the reason why it failed.

You should consider enabling DKIM and SPF record on your DNS setting, and make sure they all pass.

Some of the 3rd party vendors will likely require your Return-Path be non empty field as they might look up the address to bounce back.

From the control panel I can set the PTR record which at the moment is missing, while I can't do anything about DKIM and SPF which looks to be disabled, I will contact the hosting provider to ask if it is possible to enable them.