Running an SMTP daemon is the easy part of self-hosting email.
A production service also needs stable DNS, MX and address records, reverse DNS, TLS certificates, inbound filtering, outbound abuse controls, SPF/DKIM/DMARC, queues, backups, monitoring, account security, patching and an operational response process.
Reputation is operational
A correctly configured server is not automatically trusted by receivers. New or abused infrastructure can still encounter filtering and throttling.
Availability
Mail is store-and-forward, which gives you some resilience, but long outages eventually exhaust remote retry windows. Monitor queues and make sure DNS and certificates are not single-person maintenance tasks.