Create Your Mail System

You can turn your Synology NAS into a mail server, allowing Synology NAS users to receive and deliver mail messages.

Getting a Domain Name

The first step in setting up a MailPlus Server is to pick your new email address. An email address has two parts. The part after the @-sign is the domain name. Each domain name is owned by someone, and you are going to be the owner of your own.
Example: Amy’s email address is amy@example.com. Her domain name is example.com.

You will need to buy and register your new domain name from your ISP or third-party domain providers, then you will need to set it up in MailPlus Server. Note that MailPlus Server can handle the email for multiple domains names too.

Creating DNS Records

The second step is to create the DNS records, which help email reach your MailPlus Server. The right DNS records also help designate your MailPlus Server as a legitimate mail server. It is usually configured through your domain providers.

MX records

MX records tell the Internet where to send your domain’s email. If someone sends an email to amy@example.com, the outgoing server looks up the DNS settings for example.com. When it finds the MX record pointing to your MailPlus Server, it sends the message to your MailPlus Server.

You will need MX record for each domain for which you want to receive mail on your MailPlus Server. You can also set multiple MX records with different priorities for the same domain. This creates fallback mail servers for your domain in case the first one on the list is down. Your MX record has a domain, TTL (time to live), type (which is MX), and target domain or IP.

Reverse DNS

Many e-mail servers on the Internet are configured to reject incoming e-mails from any IP address which does not have reverse DNS. The reverse DNS for your mail server must match the hostname (FQDN) of your MailPlus Server. If your MailPlus Server’s reverse DNS and hostname do not match, email from your server may get rejected.

Setting up a Mail System with MailPlus Server

After your email domain and DNS records are ready, the rest will just follow the wizard when you launch MailPlus Server for the first time. It is here, however, that the easy flow all too often fails since new users may have no idea of not only the names and type of their mail servers, but also even what a mail server is. Please continue to read the following paragraphs to know more information.

Mail server(s)

Synology MailPlus Server offers two solutions: single-node configuration or a high-availability configuration. In single-node configuration only one Synology NAS is required to run the mail service, and it is the easiest way to set up and get going. In high-availability configuration, two Synology NAS devices form a high-availability cluster to ensure uninterrupted service when unexpected error strikes.

SMTP server

SMTP servers are the real workhorses of MailPlus Server sending thousands of messages every day. However, most ISPs block or reject mails from unknown domains. If you cannot send mails directly from your own domain, you may have to send them through well-known SMTP servers. You can configure SMTP Relay server on your MailPlus Server.

You can also map multiple domain names to MailPlus Server (e.g. synology.com, synology.com.tw, and synology.com.us) and allow users to receive mail sent to various addresses (e.g. user@synology.com, user@synology.com.tw, or user@synology.com.us).

IMAP/POP3 server

An IMAP or POP3 server handles connections from incoming IMAP or POP3 clients like Microsoft Outlook and Apple Mail. The server manages client access to the mailboxes and raw mail files so that the email is displayed in a user-friendly way.

Most servers and clients support both IMAP and POP3. POP3 clients connect to the server at specified intervals and download all of a user’s messages, without leaving copies on the server by default. POP3 was developed when most people used only one device to access one email account. IMAP is designed for multi-device users. IMAP clients send the polling request periodically to the server and IMAP mailboxes mirror the mailboxes on your MailPlus Server. IMAP and POP3 both have secure versions which use SSL encryption for mail transfer. Always use the secure version whenever possible.

The Full-Text Search feature automatically indexes mails to improve the performance of searching mails. Indexing e-mails with Chinese characters requires additional computing resource. Administrators may evaluate the user scenario and determine whether to support full-text search for Chinese mails. You can allow only certain users or groups to use Full-Text Search feature to avoid overconsumption of your system resource.

Required Ports

You should follow the table below to confirm and set up port forwarding if the network address translation (NAT) is required.

Protocols SMTP POP3 IMAP IMAPS POP3S
Port 25 110 143 993 995
Note IMAPS: IMAP over SSL/TLS
POP3S: POP3 over SSL/TLS

Firewall Settings

If you have set up the mail cluster, when any of the SMTP/SMTPS/SMTPS-TLS ports on a server are changed, you must go to DSM > Control Panel > Security > Firewall on the other server to manually modify the firewall rule ports that are related to MailPlus Server.

The firewall rules will not be automatically synced between the two servers in the mail cluster. Therefore, when a new server joins the mail cluster, you must go to DSM > Control Panel > Security > Firewall on the newly added server to manually set the corresponding firewall rules.