Cold Email API

Hey Guys, I am currently looking at a good Cold Outreach Email API to use for my cold email workflow. I built a workflow that takes a prospect, and uses a bunch of other data about this person to craft a personalized email (1 off, so each person's email is different). I want to be able to also track clicks and opens on my emails.

I have 3 domains with 4 mailboxes per domain.

As of rioght now, I have tried, MailJet (They require opt-in email addresses which doesnt work for cold outreach), Ive looked into SendGrid which didnt work, Instantly wont let you send one off emails through the API , and maybe a couple others that didnt pan out.

Does nayone know any reliable services that I can use at scale?

Thank you.