I'd like to point to another smtp server, which I am using and is much easier to set up than postfix in my opinion, especially for small servers like mine: https://www.opensmtpd.org/

I'm running a personal mailserver (opensmptd, dovecot, dkim, spf, dmarc, spamassassin) for some years now and although I initially had problems with deliverability to google there aren't any (apparent) issues so far.

Also I don't understand why people keep emphasizing google's spam filter being so much better than anything else. For my personal server SpamAssassin has proved itself to be more than sufficient, its spam filtering performance is on par with Gmail's (I have a Gmail account aswell), at least for me.

Of course, Gmails spam filter works better for the billions of accounts they manage, but in order to handle the spam of a tiny mail server I'm probably not the only person who is satisfied with SpamAssassin.