I’ve done that for several years and given up. No matter how much I honed my server config, ensured my domain had DKIM, DMARC, SPF, DNSSEC, a proper TLS certificate for both the IMAP and SMTP servers and reverse PTR records that matched, I always had deliverability issues to clients using Outlook.com/Hotmail. Sometimes Gmail as well. All config checkers gave me full marks when I sent emails, I wasn’t in a single block list, I ALWAYS had issues. I’ve given up and am paying for ProtonMail on a custom domain now, it’s not worth the headache, honestly.