To set up a Synology MailPlus mail server, the knowledge base says you need:
1. A domain name for your email address.
2. DNS records configured correctly for mail delivery.
3. MailPlus Server set up for your domain.
Key points from the sources:
- You need to buy and register a domain name from your ISP or a third-party domain provider, then set it up in MailPlus Server.
- Synology does not recommend using Synology DDNS for a mail server, because dynamic DNS may cause undelivered emails.
- MailPlus Server can handle multiple domains.
- For DNS, set up:
- an external DNS server with your domain in the MX record and the Synology NAS IP address in the A record
- an internal DNS server with the same domain in the MX record and the domain IP address in the A record
- The internal DNS priority must be higher than the external DNS priority.
- In DSM, go to Control Panel > Network > General, enable Manually configure DNS server, then enter:
- internal DNS server IP in Preferred DNS Server
- external DNS server IP in Alternative DNS Server
- In MailPlus Server go to Mail Delivery > Relay Control.
- Under Relay Inbound Mails, click Domain List, then Create, enter the rule name and domain name, and click OK.
Additional deliverability note from the guide:
- MailPlus Server checks the MX records on the two DNS servers and sends mail to the server with the higher priority.
- The Alternative DNS Server field is not available when the domain server type is AD domain or LDAP.
If you want, I can also summarize this as a short checklist.
Sources used: [7], [11]