Yeah, you are using the wrong tool if you send your newsletter from a gmail account at that scale. You can get away with a few tens of people, perhaps a few hundreds.

Above that threshold you should use tools like moosend, benchmarkemail, or similar. And they ask a pretty penny when you reach that scale.

You can’t send bulk newsletters from gmail/outlook.

Well, you can't directly, but you can use SMTP, which you can plug into any garden-variety spamming tool as long as it supports that.