Thanks, that should really have been in the main post. But does that check also include the filters that Google and Facebook likely use? I guess Facebook doesn't use Spam mail filters?
If you qualify and are willing to pay, you can use Return Path which integrates with the big providers and has visibility into where you're placed in the inbox. But in general it can be hard to even get reports when someone clicks the Spam button in Gmail! If you're a large volume sender you might be able to get into https://support.google.com/mail/answer/6254652?hl=en but in general, for smaller senders and B2B sales outreaches, it's unlikely they'll give access. Other providers have things like https://help.yahoo.com/kb/SLN3438.html which can give you granular feedback. And of course set up and monitor your DMARC feedback addresses!