Mail Delivery

General

You can set up general SMTP-related limits on users' login and inbound/outbound mail delivery.

  1. Go to Mail Delivery > General.
  2. Select Enable SMTP authentication. When connecting to Synology MailPlus Server via SMTP, clients will have to provide user credentials for login.
    Two more authentication options are available:
  3. Prohibit plaintext authentication over unencrypted connection: Using plaintext authentication increases the vulnerability because the credentials might be exposed especially on an insecure connection. Tick the checkbox to disallow plaintext authentication methods on an insecure connection.
  4. Set up an SMTP profile for Synology MailPlus Server:
  5. Click the External Postmaster button and then the plus icon to add email addresses for external postmasters. External postmaster is set to receive system emails sent to Mailer-daemon and Postmaster aliases from other mail servers.
  6. Click Apply to save the settings.

Delivery

Synology MailPlus Server can send emails through other mail servers while not being exposed to the Internet and subject to possible attacks.

To set up a general delivery rule:

You can set up a common rule for email delivery flow. Emails can be sent either directly from your Synology MailPlus Server or through a single relay host.

  1. Go to Mail Delivery > Delivery > Relay Settings.
  2. Select a rule type:
  3. Click Apply to save the settings.

To set up specific delivery rules:

You can set up dedicated rules for specific email addresses or domains. When an email fits a rule, it will be sent through the designated relay server.

  1. Go to Mail Delivery > Delivery > Relay Exceptions.
  2. Click Relay Host List.
  3. Specify rule type:
  4. Click Create.
  5. Enter the rule name and configure all the settings of the designated relay host. Select the target type and specify the targets in Recipient List or Sender List.

Relay Control

Synology MailPlus Server can send or receive emails for other mail servers.

To relay outbound mails for other mail servers:

  1. Go to Mail Delivery > Relay Control. In the Relay Outbound Mails section, click Trusted List.
  2. Click Create.
  3. Enter a rule name and specify the IP address or subnet mask of other mail servers.
  4. Click OK to save the settings.

To relay inbound mails for other mail servers:

Please set up a DNS record first and go to Domain List to add the mail server. Please refer to the following steps:

  1. Set up an external DNS server for Synology MailPlus Server.
  2. Enter your domain name in the MX record on the external DNS server and enter the IP address of Synology MailPlus Server in the A record. In this way, other mail servers will be able to send emails to MailPlus Server based on these DNS records.
  3. Set up an internal DNS server for Synology MailPlus Server to find your main mail server.
  4. Enter your domain name in the MX record on the internal DNS server and enter the IP address of the domain in the A record. The priority of the DNS records on the internal DNS server must be higher than that on the external DNS server.
  5. Go to DSM > Control Panel > Network > General. Tick the Manually configure DNS server checkbox, enter the IP address of the internal DNS server in the Preferred DNS Server field, and enter the IP address of the external DNS server in the Alternative DNS Server field to make sure the internal and external connections of Synology MailPlus Server can work properly. After Synology MailPlus Server receives emails, it will check the MX records of the two DNS servers and send emails to the mail server with a higher priority.
    Note: The Alternative DNS Server field is not available when the domain server type is AD domain or LDAP.
  6. Launch Synology MailPlus Server and go to Mail Delivery > Relay Control. In the Relay Inbound Mails section, click Domain List.
  7. Click Create.
  8. Enter the rule name and domain.
  9. Click OK to save the settings.

Note:

Security

To create blacklist and whitelist:

With the blacklist and whitelist, the system will reject, discard, or allow certain messages based on various criteria.

  1. Go to Mail Delivery > Security > Blacklist and Whitelist.
  2. Click Blacklist & Whitelist
  3. Select either rule type:
  4. Click Create.
  5. Name the rule and specify its criteria:
  6. Click OK to save the rule.

Note:

To create sender policies:

You can set policies to block emails from senders from unidentifiable domains.

  1. Go to Mail Delivery > Security > Sender Policy.
  2. Enable the following options to suit your needs:
  3. Click Apply to save the settings.

To create connection policies:

You can set policies to block client hosts that cannot be identified or may cause Synology MailPlus Server to overload.

  1. Go to Mail Delivery > Security > Connection Policy.
  2. Enable the following options to suit your needs:
  3. Click Apply to save the settings.

To create advanced security rules:

  1. Go to Mail Delivery > Security > Advanced.
  2. Enable the following options to suit your needs:
  3. Click Apply to save the settings.