Knowledge Center

Domain

You can manage multiple domains and configure settings related to alias, auto BCC, usage limit, and disclaimer in Synology MailPlus Server.

To add a domain:

  1. Click Add.
  2. Enter the following information and click Next:
    • Domain name: Specify a domain name (e.g., abc.com). Make sure the domain name matches the hostname of the DNS server.
      Note: Internationalized email addresses and header information in non-ASCII characters (e.g., Chinese and Russian) are supported. You can also set rules for Alias and other features in non-ASCII characters.
    • Description: Enter a description for the domain.
    • Default email address format: Synology MailPlus Server will fetch account information based on the specified format and use the information and the domain name to compose the email address.
      The table below shows the default settings Synology MailPlus Server provides for each account type at Service > SMTP:
      Account type Default setting
      Local user Account name
      Mail nickname
      LDAP user Account name
      Mail nickname
      Domain user Account name
      Display name
      Mail nickname
      Email

      In addition to the above options, you can select Custom to customize the default email address format in the Custom variables field.

      The following table shows the variables that Synology MailPlus Server supports:

      Variable Value
      <a> Account name
      <g> Given name
      <i> Middle initial
      <s> Surname
      <d> Display name
      <m> Mail nickname
      <xa> Uses the first x letters of the account name.
      For example, if x = 2, the first two letters of the account name will be used.
      <xs> Uses the first x letters of the surname.
      For example, if x = 2, the first two letters of the surname will be used.
      <xg> Uses the first x letters of the given name.
      For example, if x = 2, the first two letters of the given name will be used.
      <custom_attribute> Fetches the value corresponding to the variables you set. Please refer to the table in the following paragraph to see the supported variables of each account type.

      Synology MailPlus Server supports using multiple variables to form the default email address format. For example, the following is the information of a domain user:

      • Account name: Administrator
      • Display name: andrewfan

      If you enter "<a>_<d>" in the Custom variables field, Synology MailPlus Server will use "Administrator_andrewfan" as the user's email address.

      Supported variables vary according to different account types set at Service > SMTP. For details, please refer to the table below:

      Variable Local user LDAP user Domain user
      <a> O O O
      <g> X X O
      <i> X X O
      <s> X X O
      <d> X X O
      <m> O O O
      <xa> O O O
      <xs> X X O
      <xg> X X O
      <custom_attribute> X O O
    • Add new users automatically to this domain: Synology MailPlus Server will fetch information according to the Default email address format to compose new users' email addresses.
  3. Select members to add to this domain and click Next.
  4. Confirm the email addresses of the selected members.

Note:

  • All variables should be within "< >".
  • If you want to use multiple variables, put a "_" between each variable.
  • Illegal characters include space and control characters. Synology MailPlus Server will remove any illegal characters from the fetched information.
  • Synology MailPlus Server will use account names to form email addresses if it cannot fetch any information according to the Default email address format.
  • Editing account names will not change the existing email addresses.

To edit domains:

  1. Select the target domain and click Edit.
  2. Go to the General tab to adjust the following settings:
    • Domain name: Edit the domain name or click Additional Domain to create a domain alias.
    • Description: Edit the domain description.
    • Default email address format: Select a format from the drop-down menu.
    • Add new users automatically to this domain
  3. Save the settings.

To enable DKIM signing:

  1. Select the target domain and click Edit.
  2. Click Advanced.
  3. Tick Enable DKIM signing on outbound emails.
  4. Enter a DKIM selector prefix as you please. A DKIM selector is a name used for the identification of the DKIM public key.
  5. Click Generate Public Key.
  6. Select the DKIM key length. The default is 2048 bits. Note that 2048-bit keys may exceed the limit set by your domain host. If the DKIM key gets rejected, change the key length to 1024 or 512 bits.
  7. Click OK to save the settings.
  8. Add and update the public key to your DNS records using a TXT record, so that other mail servers will be able to authenticate your DKIM signature.
    • The TXT record should be added as follows:
      • Type: TXT
      • TXT record name: DKIM selector prefix._domainkey.your domain
        Note: DKIM selector prefix is the prefix you entered above, and your domain is your actual domain name.
        Example: 123._domainkey.example.com
      • TXT record value: v=DKIM1; k=rsa; p=DKIM public key
        Note: DKIM public key is the key you generated in the above step.
        Example: v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQE...
      Type Name Value
      TXT 123._domainkey.example.com v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQE...
    • A 2048-bit DKIM public key may exceed the 255-character string limit set by most domain providers. You can split the public key into parts of 255 characters or less to overcome the limit. You have to add two TXT records as follows:
      Type Name Value
      TXT 123._domainkey.example.com v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQE...
      TXT 123._domainkey.example.com pZ7lDaAXXwLYjN91YY7ARbCEpqapA9Asl854BCHMA7L...
      Note: "v=DKIM1; k=rsa; p=" can be omitted in the second record. You only need to type the rest of the public key.

Note:

  • When Skip authentication for local network connections from terminal at Mail Delivery is enabled, even if users in the local network do not have an account and a password, they can still send emails from the terminal but the emails will not carry the DKIM signature.
  • If you have listed IP addresses on the whitelist at Mail Delivery > Security > Blacklist and Whitelist, users without accounts and passwords can still send emails through the IP address of the terminal. However, the sent emails will not carry the DKIM signature.
  • If you want outbound emails to carry the DKIM signature, go to Security > Authentication > DKIM and click Whitelist to specify an internal host or a subnet. Then, all outbound emails of this domain, that are sent from the specified source via Synology MailPlus, a third-party mail client, or a terminal, will carry the DKIM signature.

To enable catch-all:

  1. Select the target domain and click Edit.
  2. Click Advanced.
  3. Tick Enable catch-all to receive emails that are sent to an address that does not exist or is not enabled in the domain.
  4. Select a user account to serve as the catch-all mailbox.

To add users to a domain:

  1. Select a domain and click Edit.
  2. Go to the User tab and click Add.
  3. Select the target users and click Next.
  4. Confirm the email addresses of the selected users.

To edit user settings in a domain:

  1. Select a domain and click Edit.
  2. Go to the User tab, select the target user, and click Edit.
  3. In the Edit User window, adjust the following settings:
    • Role: Select a role from the drop-down menu.
      • Domain administrator: Domain administrators can manage all domain settings except for creating and deleting domains.
      • Regular user: Regular users cannot manage domain settings.
      • Follow group settings
    • Email address: Enter email addresses in this field. Emails sent to these addresses will be delivered to the mailbox of this account.

Note:

  • The role settings will not affect system administrators' privileges.
  • If the user belongs to multiple groups in the domain, the priority will be as follows: Domain administrator > Regular user.

To remove users from a domain:

  1. Select a domain and click Edit.
  2. Go to the User tab, select the target users, and click Delete.

To add groups to a domain:

  1. Select a domain and click Edit.
  2. Go to the Group tab and click Add.
  3. Select the target groups and click Next.
  4. Confirm the email addresses of the members.

To edit group settings in a domain:

  1. Select a domain and click Edit.
  2. Go to the Group tab, select the target group, and click Edit.
  3. In the Edit Group window, if you select Domain administrator from the Role drop-down menu, all the users in this group will have the same permissions as the Domain administrator.

To remove groups from a domain:

  1. Select a domain and click Edit.
  2. Go to the Group tab, select the target groups, and click Delete.

To view members:

  1. Select a domain and click Edit.
  2. Go to the Group tab and click View members to check if certain users belonging to the group are not in the domain.

To create an email alias:

You can configure email aliases to group email addresses of specific users, groups, and aliases. When sending emails, users can quickly specify recipients using aliases without entering multiple addresses. Follow the steps below to create an email alias:

  1. Select a domain and click Edit.
  2. Go to the Alias tab and click Create.
  3. Name the new alias in the Alias name field. If the alias carries the same name as an email account's username, the account cannot be automatically added as an alias member.
  4. Select from the drop-down menu to view aliases, users, groups, or external mailboxes. Add the desired ones to the alias.
  5. Click OK to save the settings.

To import/export aliases:

  1. Select a domain and click Edit.
  2. Go to the Alias tab and click Tools at the top to perform the following:
    • Import aliases: Import a postfix file containing email aliases.
    • Export aliases: Export email aliases into a postfix file.

To create an auto BCC rule:

When an inbound or an outbound email matches any auto BCC (Blind Carbon Copy) rules, a BCC email will be automatically created and forwarded to the specified address. This helps users back up important emails and protect recipient privacy. Follow the steps below to create an auto BCC rule

  1. Select a domain and click Edit.
  2. Go to the Auto BCC tab. Click Create to define the trigger conditions:
    • 'From:' address contains: Creates a BCC email when an email comes from the specified address.
    • 'To:' address contains: Creates a BCC email when an email goes to the specified address.
    • All messages: Creates a BCC email whenever receiving or sending an email.
  3. In the Send BCC to this address field, specify an email address, a username, or an email alias to forward BCC emails to.
  4. Click OK to save the rule.

To import/export an auto BCC rule:

  1. Select a domain and click Edit.
  2. Go to the Auto BCC tab and click Tools on the top to perform the following:
    • Import sender rules: Import a postfix file containing rules based on sender addresses.
    • Import recipient rules: Import a postfix file containing rules based on recipient addresses.
    • Export sender rules: Export a postfix file containing rules based on sender addresses.
    • Export recipient rules: Export a postfix file containing rules based on recipient addresses.

To configure sending limits and daily quotas:

  1. Select a domain and click Edit.
  2. Go to the Usage Limit tab. In the Sending Limit section, adjust the following settings:
    • Maximum size per email (MB): Specify the size limit of an outbound email.
    • Enable size limit on single attachments: Tick this option to specify the size limit for a single attachment and enter a value in the Size limit (MB) field below.
    • Disable auto forwarding
  3. In the Daily Quota section, adjust the following settings:
    • Enable daily sending quota: Tick this option to limit the number of outbound emails a user can send per day.
    • Enable daily traffic limit on outbound email: Tick this option to limit the total size of outbound emails a user can send per day.
    • Outbound Usage: Click this button to view the outbound email usage of an individual user.
  4. Click OK to save the settings.

Note:

  • Users exceeding the limit will not be able to send outbound emails until the next day.
  • Synology MailPlus web client has a limit of 100 MB per attachment. We recommend using a shared link when the file size exceeds the limit.

To create a disclaimer rule:

The system can automatically append a custom disclaimer to outbound emails to clarify legal obligations/agreements or to promote a campaign.

You can customize rules to specify when a disclaimer should be appended.

  1. Select a domain and click Edit.
  2. Go to the Disclaimer tab and click Create.
  3. Go to the Rule tab and enter the following information:
    • Name: Specify a name for the disclaimer.
    • Do not append this disclaimer when all recipients are from this domain: Tick this option so that the disclaimer will not be appended to emails sent to users in the email domain of Synology MailPlus Server.
  4. Specify matching rules to define when to append the disclaimer to an outbound email:
    • match the following rule: Select All to append the disclaimer when all matching rules are met. Select Any to append it when at least one of the matching rules is met.
    • Sender and Recipient: Append the disclaimer when an outbound email is received by or sent from the specified user/group or email address.
    • To add more matching rules, click +. To delete unwanted ones, click -.
  5. Specify exception rules to define when not to append the disclaimer to an outbound email:
    • Sender and Recipient: Do not append the disclaimer when an outbound email is received by or sent from the specified user/group or email address.
    • To add more exception rules, click +. To delete unwanted ones, click -.
  6. Go to the Content tab to draft the disclaimer:
    • HTML text: Create HTML content with the text-editing tools on the top toolbar. The content specified here will show up in outbound HTML emails.
    • Plain text: Enter plain-text content or click Copy from HTML text to convert the HTML content to plain-text. The content specified here will show up in outbound plain-text emails.
  7. Click OK and then Save to save the disclaimer.
  8. Disclaimers that rank higher have higher priority than the ones that rank lower. To change the priority, select a disclaimer and drag and drop it to a suitable position.

Note:

  • The disclaimer will not be appended when an outbound email meets any exception rules.

To delete a domain:

  • Select the target domains and click Delete.

Note:

  • Primary domains cannot be deleted.

To set a primary domain:

  • Select the target domain and click Primary.