How to set up SPF, DKIM, and DMARC for your sending domain
mailfully.com/blog/spf-dkim-dmarc-setup
What Jamie wrote
Very few people manage their own domains for email. I do for multiple domains. It isn't simple but it also isn't that hard. This is a good overview if you ever want to move off of free email. Fastmail is what I use and they have a great step-by-step for this as well.