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 MailPlus Server via SMTP, clients will have to provide user credentials for login.
3. Two more authentication options are available:
   • Skip authentication for local network connections from terminal: Without login credentials, clients in MailPlus Server's local network can directly receive and send emails using a terminal.
   • Sender name and login name must be identical: When sending emails, the logged-in user has to use a sender name identical with the login username.
4. To stop SMTP clients from auto-forwarding emails, select Disable auto forwarding.
5. Set up an SMTP profile for MailPlus Server:
   • Domain name: Specify the domain name (e.g. abc.com) for MailPlus Server; to create domain aliases for this domain, click Additional Domain. Make sure the domain name and domain aliases are matched to a hostname in the DNS server.
   • Hostname (FQDN): Specify the hostname of MailPlus Server in the FQDN format. Make sure the hostname is matched to the IP address in the DNS server.
   • SMTP banner: Specify the text that will show up on an SMTP client's Telnet terminal.
   • Max recipients per message: Set the maximum number of recipients in an inbound/outbound message. A message exceeding the limit will be rejected.
   • Max message hops: Set the maximum number of hops (i.e. mail relays) made by an inbound/outbound message. A message exceeding the limit will be rejected.
   • Maximum size per email (MB): Set the maximum size of an inbound/outbound message. A message exceeding the limit will be rejected.
   • Enable size limit on single attachments: Set the maximum size of each attachment in an inbound/outbound message. A message exceeding the limit will be rejected.
6. Click Apply to save the settings.

Delivery

You can have MailPlus Server relay its emails to a third-party mail server for successful delivery when it has been blocked or not correctly identified by client hosts.

1. Go to Mail Delivery > Delivery.
2. Select Enable SMTP Relay and specify the following settings:
   • Server: Specify the IP address or hostname of a relay server for MailPlus Server.
   • Port: Specify the port of the relay server for receiving emails from MailPlus Server.
   • Always use a secure connection (TLS): Enable this option to relay emails through TLS-protected connection.
   • Authentication required: Enable this option when the relay server requires login credentials, and provide a set of correct username and password.
3. Click Apply to save the settings.

Security

To create black and white lists:

With the black and white lists, the system will reject, discard, or allow certain messages based on various criteria.

1. Go to Mail Delivery > Security > Black and White Lists.
2. Select either rule type:
   • Blacklist: Set rules to reject/discard matching email messages.
   • Whitelist: Set rules to allow through matching email messages.
3. Click Create.
4. Name the rule and specify its criteria:
   • IP: Specify a sender IP address (e.g. 192.163.1.1).
   • IP/subnet mask: Specify a sender IP address and its subnet mask (e.g. 192.163.1.1/255.100.10.1).
   • Sender: Specify a sender address (e.g. 123@abc.com).
   • Recipient: Specify a recipient address (e.g. 456@abc.com).
   • Domain (for whitelist rules): Specify a sender domain (e.g. abc.com).
   • Do this (for blacklist rules): Select the action against a matching message:
     • Reject it: Ban a matching message from passing through MailPlus Server.
     • Discard it: Abandon a matching message without informing the sender.
5. Click OK to save the rule.

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:
   • Reject senders without fully qualified domain name (FQDN): Bounce emails when senders are from a domain without an FQDN.
   • Reject senders using unknown domains: Bounce emails when intended recipients are not existing MailPlus Server users and when the sender domain does not have a valid DNS entry.
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 MailPlus Server to overload.

1. Go to Mail Delivery > Security > Connection Policy.
2. Enable the following options to suit your needs:
   • Reject unknown client hostnames: Block client connections from a host without an analyzable IP or hostname.
   • Keeping more concurrent connections than the limit: Set the maximum number of concurrent connections from a client host. When the limit is reached, extra connections will be blocked.
   • Sending more messages than the limit in one minute: Set the maximum number of outbound messages sent from a client host in one minute. When the limit is reached, the client host will be blocked until next minute.
   • Building more connections than the limit in one minute: Set the maximum number of connections built by a client host in one minute. When the limit is reached, the client host will be blocked until next minute.
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:
   • Reject unauthorized pipelining requests: Block client connections that keep sending SMTP commands to avoid system overload.
   • Reject HELO hostnames without fully qualified domain name (FQDN): Reject connections from hosts that send a HELO/EHLO command and do not have an FQDN hostname.
   • Reject unknown HELO hostnames: Reject connections from hosts that send a HELO/EHLO command and do not have a valid DNS entry.
   • Block any IP emailing more non-existent accounts than the limit: Set the maximum number of non-existent MailPlus Server accounts that an IP can send email to. When the limit is reached, the IP will be blocked until next day.
   • Max junk commands per session: Set the maximum number of junk commands (i.e. noop, vrfy, etrn, and rset) that a client connection can send before sending email. Every 10 junk commands will cause one-second delay on mail delivery.
3. Click Apply to save the settings.

Alias

You can set up aliases to cover email addresses of specific users, groups, and aliases. When sending emails, users can quickly specify intended recipients using aliases without entering numerous addresses.

To create email aliases:

1. Go to Mail Delivery > Alias.
2. Click Create to define an alias and its included members:
   • Alias name: Specify the name for the alias. If the alias is identical to a username, the username cannot be added to the alias.
   • External mail box: Specify an external email address for the alias. Emails sent to the alias will be redirected to the specified address.
3. View users, groups, or aliases using the top-right menu, and add desired ones to the alias by selection.
4. Click OK to save the alias.

To import/export aliases:

1. Click Tools on the top
2. Select from the following options:
   • Import aliases: Import a file in the Postfix format containing email aliases.
   • Export aliases: Export created aliases into a Postfix format.

Auto BCC

When inbound or outbound messages match any auto BCC (Blind Carbon Copy) rule, a BCC will be automatically created and forwarded to a specified address, allowing users to back up important messages and protect recipient privacy.

To create auto BCC rules:

1. Go to Mail Delivery > Auto BCC.
2. Click Create to create an auto BCC rule and define its trigger condition:
   • 'From:' address contains: When an inbound message comes from the specified email address, it will have a BCC.
   • 'To:' address contains: When an outbound message goes to the specified email address, it will have a BCC.
   • All messages: All inbound and outbound messages will have a BCC.
3. In Send BCC to this address, specify an email address, username, or email alias to forward the BCC to.
4. Click OK to save the rule.

To import/export auto BCC rules:

1. Click Tools on the top.
2. Select an option from the menu:
   • Import sender rules and Import recipient rules: Import a postfix file containing rules based on sender/recipient addresses.
   • Export sender rules and Export recipient rules: Export a postfix file containing rules based on sender/recipient addresses.

Daily Quota

You can limit the number and total size of outbound messages each user can send out every day. Users exceeding any limit will not be allowed to send outbound messages until next day.

1. Go Mail Delivery > Daily Quota.
2. You can enable the following limits on each user's daily outbound messages:
   • Enable daily sending quota: Select to limit the number of outbound messages a user can send daily.
   • Enable daily traffic limit on outbound email: Select to limit the total size of outbound messages a user can send daily.
3. To view each user's outbound email usage, click Outbound Usage.
4. Click Apply to save the settings.

Disclaimer

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

To set up disclaimer rules:

You can set up custom rules to decide whether a disclaimer should be appended to outbound messages.

1. Go to Mail Delivery > Disclaimer.
2. Click Create.
3. Go to Rule to provide basic disclaimer information:
   • Name: Specify the name for the disclaimer.
   • Do not append this disclaimer when all recipients are from this domain: Select this option so that the disclaimer will not be appended to messages sent to users in MailPlus Server's mail domain.
4. Specify matching rules to define when to append the disclaimer in outbound messages:
   • matching the following rule: To append the disclaimer when all matching rules are met, select All. To append it when at least one matching rule is met, select any.
   • Sender and Recipient: Decide when to append the disclaimer when an outbound message is received by or sent from a 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 in outbound messages:
   • Sender and Recipient: Decide when not to append the disclaimer when an outbound message is received by or sent from a specified user/group or email address.
   • To add more exception rules, click +. To delete unwanted ones, click -.
6. Go to Content to specify the disclaimer content:
   • HTML text: Create the HTML content with the text-editing tools above. The content specified here will show up in outbound HTML messages.
   • Plain text: Create the plain-text content, or click Copy from HTML text to convert the HTML content for use. The content specified here will show up in outbound plain-text messages.
7. Click OK and then Save to save the disclaimer.
8. Higher disclaimers have more priority than lower ones. To change their priority, select a desired one and drag and drop it to a suitable position.