Mac Mail lets you View --- Message --- All Headers
This is a bunch, but it shows every stop along the way, especially the sender's address.
(or source, which can be enormous)
You can also drag the message to a folder and drag and drop it here (read the privacy noticel)
https://www.securitytoolkits.com/tools
This tool
https://www.securitytoolkits.com/tools/email-header-analyzer
I just found it today.
Normally, I read headers because I was an email hotshot in various jobs, but this is a lot for "normal" people.
You'll probably find two kinds of garbage emails.
1. Just people selling stuff from a list of email addresses that they bought or stole
2. Serious phishing emails. Key things to look for are "CLICK HERE" (often downloads malware) or SIGN INTO YOUR ACCOUNT, which captures you password at some site.
Gorge.net - Blue Mountain Networks High Speed Internet - Local Provider
Gorge.net is a domain that redirects users to Blue Mountain Networks, a local internet service provider specializing in high-speed internet solutions for both residential and business customers.
Could be a home computer user infected with malware and sending out emails that aren't from a known phishing domain. Just a guess.
I'd want to see headers but that would divulge more info than you want to share in public.