Copying my reply to HN:

Some feedback: you should add a PTR record (reverse DNS) for studer.dev and mail.studer.dev.

I also noted that your DMARC record has p=quarantine, which depending on the details of your outgoing setup, may cause your emails to be placed in the spam folder if DMARC fails for any reason. I generally advise against using DMARC with any policy other than `v=DMARC1; p=none` or else you're liable to run into issues, it's not a very good standard.

Otherwise, your configuration looks good to me. Also try https://www.mail-tester.com to see what they think.