⚖️Load balancing

Postal route load balancing has three primary use cases:

Contact List Domain Grouping

Route mailbox providers that have multiple domain names sharing a common email infrastructure through an API, SMTP Relay, or MTA delivery policy optimized for them using contact list domain routing.

Optimizing for deliverability

Route important mailbox providers like Gmail through the API, SMTP Relay, or MTA delivery policy where you're getting the best deliverability*.


Distribute your outgoing mail across multiple API, SMTP Relay, or MTA delivery policies based on percentage allocation and warmup status.

*Delivery is when a message is successfully delivered, Deliverability is when the message hits the inbox.

One sender email address using multiple email service providers

The email address configured in your broadcast or funnel will be used when load balancing multiple API or SMTP Relay connections.

This email address will likely need to be authenticated with each email service provider first.

Contact list domain routing will be disabled by default with the default setting of "All Domains in Contact List" sending all mail through one route.

To route your mail based on the mailbox provider's domain, click Add Domain Route.

Use the dropdown to select a domain group you've created previously.

Select an alternative path for delivering mail to this domain.

Repeat until your postal route is fully optimized according to your delivery strategy.

Use partitioning to split your email for the same domain group across multiple email service providers or MTA delivery policies.

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