You don't need to use a delivery service. It's true you need to set up SPF/DKIM/DMARC for many peers to accept mail from you, but then you can deliver the mail yourself directly.
After using the same Digital Ocean IP for 8 years, I got unlucky and their /24 block got listed on spamhaus (or mailcop, or similar) and major providers (Outlook and Gmail) stopped accepting messages from my server.
It works great until it doesn't