Setting Up the Email Filter-Only Service

The OpenSRS Email Filter-Only Service is a low-cost mail filtering service for service providers. It sits between your mail servers and the internet, acting as a gateway that protects your users and infrastructure from spam and viruses. This article walks you through setting it up in the Reseller Control Panel or the Mail Administration Console (MAC).

About the filter-only service

The filter-only service scans every message and decides whether it is legitimate or contains spam, a phishing attempt, or a virus. Legitimate mail is delivered to the recipient's inbox. Spam can be tagged in the subject line and given a custom header so your existing mail server can route it to a spam folder, or it can be held in a web-based Spam Quarantine where recipients sign in to review flagged messages. Messages that contain a virus are discarded.

You filter mail for a domain whose mailboxes still live on your own mail server. OpenSRS does not host the mailboxes in this setup; it screens inbound (and optionally outbound) mail and then hands clean mail to the destination server you specify.

How implementation works

Setting up the filter-only service follows the same overall sequence whether you use the Control Panel or the MAC:

1. Create a domain profile for the domain you are filtering.
2. Create a filter-only account for every email address on your mail server.
3. Set up the web-based spam portal with a CNAME record (if you are quarantining spam).
4. Set up outbound mail filtering, if you want it.
5. Inform your users about the new anti-spam system.
6. Change the domain's MX record to point at the OpenSRS filter service.
7. Test that mail flows through the filter to your server.

Setting up in the Control Panel

Step 1: Create a new domain

Create a domain profile so the filter service knows to handle the domain's mail flow. This is also where you set domain-wide options such as the location of your mail server.

1. In the Email section of the Control Panel, click the Email Domains tab.
2. Click the plus sign (+) at the top of the page.
3. Enter the domain name in the text field, then click Add.
4. On the Settings tab, click Edit in each section to set the related fields, then click Save.

Make sure you complete these fields:

Step 2: Create anti-spam filter-only accounts

Every email address on your mail server needs a matching account in the filter-only system. This enables the anti-spam filter and lets valid mail pass through. You can create accounts one at a time or in bulk.

To create a single filter account:

1. In the Email section, click the Email Domains tab, then click the domain under which you want to create the user.
2. Click the plus sign (+).
3. On the Add a User page, enter the user name, then click Add. The User Settings page opens.
4. In the Mailbox User section, click Edit.
5. In the Type field, choose Filter. The remaining fields are optional.
6. Click Save.

To create filter accounts in bulk:

1. In the Email section, click the Email Domains tab.
2. Click the domain you want to edit, then click the Bulk Tools tab.
3. Click the button beside Bulk Add.
4. Enter one account per line in the form user@domain.com,filter,password,,,Firstname,Lastname, where first and last name are optional. For example: john@mydomain.com,filter,abc123!,,,John,Moore,
5. Click Submit.

Step 3: Set up your anti-spam portal

If you chose to quarantine spam, give your users a portal where they can sign in to review captured spam and release messages flagged in error. If you set Filter Delivery to passthrough, you do not need a portal: all spam is delivered to your server with added identifying information.

To create a portal, add a CNAME record in your DNS that points a hostname on your domain to the OpenSRS server. For example.com, a portal at portal.example.com looks like:

portal.example.com in cname mail.example.com.cust.<cluster>.hostedemail.com

Step 4: Set up outbound mail filtering

Filter accounts can send mail through the OpenSRS SMTP service. Signing in requires the user's full email address and password (SMTP AUTH). You can reuse the portal CNAME for SMTP or add a dedicated record:

smtp.example.com in cname mail.example.com.cust.<cluster>.hostedemail.com

Users then set their mail client's outbound server to smtp.example.com so outbound mail is scanned for spam.

Step 5: Inform your users about the new anti-spam system

Tell your users that mail flow to their accounts is changing. If you use the quarantine system, give them the portal address, their username and password, and instructions for managing safe and block sender lists and releasing quarantined mail. If you pass spam through, explain how they can identify it, such as a modified subject line or extra header information.

Step 6: Update the MX record

Once accounts are created and Filter MX Host points to your destination server, update the domain's MX record so all incoming mail passes through the OpenSRS anti-spam system before reaching your server:

example.com. IN MX 0 mx.example.com.cust.<cluster>.hostedemail.com

Step 7: Confirm mail is accepted by your mail server

After changing the MX record, send test mail to confirm it reaches your server. If it does not arrive, check the web-based Spam Quarantine to see whether it was flagged, and review your mail server's connection and delivery logs.

Setting up in the MAC

Step 1: Create a new domain in the MAC

Create a domain profile so the filter service handles the domain's mail flow and you can set domain-wide options.

1. In the navigation pane, click Add Domain. The Create Domain page appears.
2. Complete the fields below.
3. Click Create.

Step 2: Create anti-spam filter-only accounts

Create a filter-only account for every address on your mail server. A filter account works as a spam quarantine, trapping spam and letting good mail flow to the matching account on your server.

To create a single filter-only mailbox:

1. In the navigation pane, click Add User.
2. In User, enter a name and press Enter. The other fields stay disabled until you do this.
3. In Password, set the password for the user's Quarantine Portal.
4. In Type, choose Filteronly. The remaining fields are optional.
5. Click Create, or Create & Repeat to add another user without closing the window.

To create filter accounts in bulk:

1. In the navigation pane, click Bulk Action.
2. Keep the operation set to Add.
3. Enter one account per line in the form user@domain.com,filter,password,,,Firstname,Lastname, where first and last name are optional. For example: john@mydomain.com,filter,abc123!,,,John,Moore,
4. Click Process.

Steps 3 to 7: Portal, outbound filtering, users, MX, and testing

The remaining steps in the MAC are identical to the Control Panel: set up the anti-spam portal, configure outbound mail filtering, inform your users, update the MX record, and confirm mail is accepted by your server. See those steps under Setting up in the Control Panel above for the CNAME and MX record examples.

Next steps

• Confirm your cluster. You need it for every CNAME and MX record. See Which Email Cluster Am I On?
• Review your DNS records. For the full list of record types and allowlist IPs, see Configuring DNS for OpenSRS Hosted Email.
• Manage domain aliases. If you filter multiple domains, see Adding and Removing Domain Aliases.

Questions? Contact OpenSRS Support.