If it’s a matter of the domain being “warmed up” then I basically have no chance. This is unfair.
Yes it is very unfair. Gmail is basically incentivizing you to send thousands of mails or use hacks like inbox warmups. The same happens for SEO when you have to care more about backlinking and keywords than actual content.
Unfortunately there is nothing you can do about it. It's how things are at the moment :/
I can speak up about it. Others can too. We don’t have to live under these conditions.
It's a good thing that it's very hard to send lots of mails to strangers
Spammers do everything you do and a lot more, yet most of them are blocked(and just imagine what would happen if they could send as many mails as they want without going through all those hoops, we'd get basically nothing but spam)
The only reasonable solution if you're not a big/reputable business is to use a service like mailgun/mailjet/mailchimp/sendgrid, for a small business it would cost next to nothing(or even just 0$, if you can get some free credits or a small free plan)
It will save you a lot of headaches