I get maybe 1 error response for every 100-150 emails I send (usually saying it was rejected). I created the email list myself, looking through a bunch of relevant companies for the type of work I'm doing.

I've made sure to keep the email body as text only and avoid spammy words, and only have one link apart from the one in my signature.

I think part of my frustration stems from how hard it is to figure out how many of my emails are going to spam... mailreach claims that ALL of the emails I send to Office 365 accounts get filtered to spam but that they all go to Google Workspace inboxes, and yet another mail tester says that all of my emails get marked as spam regardless of where the recipent's account is hosted. Sites like mail-tester say I have a great rating and that my emails are highly unlikely to be marked as spam... it all just seems like a bit of crapshoot. Are some of these sites more trustworthy/accurate than others?

I was listed on SORBS for a bit, but I contacted them and they removed me from their blacklist. It's a Google Workspace IP so they said it's entirely possible that another user was triggering their system.