Delivery to Multiple Servers

Email delivery is normally done to a single mail server. If you have multiple servers that you would like our filters to deliver emails to, this will require some additional configuration.

This article applies to Administrator accounts - Quarantine Administrator accounts can view this information but cannot edit the parameters.

Administrators can manage delivery settings for their domains under:
My Organization → Parameters → Inbound Filtering → Domains

Understanding Multi-Host Delivery Configuring Load Balanced Delivery
Configuring Fail-over Delivery How To Configure

Understanding Multi-Host Delivery

By default, Cumulus only allows a single hostname or IP address to be configured as the destination for filtered mail and will try to deliver it directly to the machine which answers at that address. As such, the delivery process looks like this:

There may be situations where you want to be able to split your incoming traffic across multiple servers to reduce load or deliver to an alternative server if your main server goes down. To do so, we leverage the very same mechanism we use to ensure reliability for your filtering: MX records. Instead of pointing Cumulus directly to a single server, we will instead tell it to look for a set of MX records for the hostname in your Transport field and use those results for delivery instead.

Let's suppose you wish to set up delivery to multiple servers for your domain "". First, you will need to choose a hostname where you can put the records we will be checking for delivery. In this example, let's use "". The specific MX records you will need to create will depend if you're looking for a load balancing or a fail-over setup:

Configuring Load Balanced Delivery

In the case of load balanced delivery, the traffic will be delivered equally on all the servers shown with the same priority number.

Configuring Fail-Over Delivery

In the case of fail-over delivery, email delivery will occur on the server with the lowest priority. If delivery isn't possible to this server, email delivery will continue on the server with the next-lowest priority.

How To Configure

Make an inventory of all the servers that should accept emails for your domain.
Create a new entry in your DNS zone that will contain all the servers as MX records.
  • The entry should exist as a sub-domain (eg.:
  • Add the mailservers as MX records to this sub-domain.
  • Determine what priority the MX records should have depending on whether you want a load balancing or fail-over configuration.
Connect to your Cumulus account.
Head to your domains parameters under Parameters → Inbound Filtering → Domains.
Select the domain you want to modify by clicking its View link.
Modify the parameters as follows:
  • Click the Edit link in the Domain Information section.
  • Change the domain's Transport to the new sub-domain (eg.:
  • Activate (✔️) the Use the hostname's MX record parameter.
Click the Save button. The configuration can take up to 5 minutes to apply.