You can turn your Synology NAS into a mail server, allowing Synology NAS users to receive and deliver mail messages.
This article will give you basic information on how Synology MailPlus Server works and what you need for the setup of MailPlus Server. If you need step-by-step instructions, please refer to this article.
The first step in setting up a Synology MailPlus Server is to pick your new email address. An email address has two parts. The part after @ indicates the domain name.
Example: Ann's email address is "ann@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 and set it up in Synology MailPlus Server. Note that Synology MailPlus Server can handle emails for multiple domain names.
The second step is to create the DNS records, which help emails reach your Synology MailPlus Server. The right DNS records also help designate your Synology MailPlus Server as a legitimate mail server. It is usually configured through your domain providers.
Mail exchanger record (MX record) indicates where emails should be routed to. You have to set up an MX record pointing to your mail server so that the Internet will know where to send your emails. A domain can have more than one mail server, so you can set up multiple MX records for a domain with multiple mail servers and further configure MX record priorities. The lower the preference number is, the higher the priority will be. For example, to make sure ann@example.com works, you have to set up an MX record pointing to the mail server, which should receive emails on behalf of the domain "example.com".
Address records (A records) are a type of DNS records that point a domain or subdomain to an IP address. You have to point the A record to the IP address of your Synology NAS if you want to receive emails on your Synology MailPlus Server.
Reverse DNS helps a mail server find out the hostname or domain behind an IP address. Many mail servers use reverse DNS to determine whether the sender's domain name is associated with spammers. Therefore, emails sent from an IP address that does not have reverse DNS are likely to be rejected. Please note that the reverse DNS for your mail server must match the hostname (fully qualified domain name, FQDN) of your Synology MailPlus Server. If your Synology MailPlus Server's reverse DNS and hostname do not match, emails from your server may be treated as spam.
After your email domain and DNS records are ready, you can just follow the wizard when you launch Synology MailPlus Server for the first time. However, the easy flow often fails since new users may have no idea of not only the names and type of their mail servers but also what a mail server is. Please continue to read the following paragraphs to know more about the structure of a mail server.
Synology MailPlus Server offers two solutions: a single-node configuration or a high-availability configuration. In the 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 the high-availability configuration, two Synology NAS devices form a high-availability cluster to ensure uninterrupted service when an unexpected error strikes.
SMTP servers are the real workhorses of Synology MailPlus Server sending thousands of messages every day. However, most ISPs block or reject emails from unknown domains. If you cannot send emails directly from your domain, you may have to send them through well-known SMTP servers. You can configure the SMTP relay server on your Synology MailPlus Server.
You can also map multiple domain names to Synology MailPlus Server (e.g., example.com, example.com.tw, and example.com.us) and allow users to receive emails sent to various addresses (e.g., user@example.com, user@example.com.tw, or user@example.com.us).
An IMAP or POP3 server handles connections from incoming IMAP or POP3 clients such as Mozilla Thunderbird, Microsoft Outlook, and Apple Mail. IMAP and POP3 servers grant clients access to the emails saved on the mail server.
Most mail servers and clients support both IMAP and POP3. POP3 applies to users with a single device while IMAP is dedicated to users with multiple devices. POP3 clients download emails from the server and save them locally. IMAP clients modify emails on the mail server, which will be mirrored to all the IMAP client mailboxes; therefore, all the changes made to an email will be synchronized across multiple devices.
To secure the data transfer via IMAP and POP3 connection, we recommend that you use SSL and TLS encryption.
The Full-Text Search feature automatically indexes emails to improve the performance of searching emails. Indexing emails with Chinese characters requires additional computing resources. Administrators may evaluate the user scenario and determine whether to support full-text search for Chinese emails. You can allow only certain users or groups to use Full-Text Search feature to avoid overconsumption of system resources.
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 |
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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 Synology 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.