> For the complete documentation index, see [llms.txt](https://docs.emaildelivery.com/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.emaildelivery.com/docs/advanced-postal-route-configuration/load-balancing.md).

# Load balancing

Postal route load balancing has three primary use cases:

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**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](/docs/advanced-postal-route-configuration/contact-list-domain-routing.md).
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**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**\*.**
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**Partitioning**

Distribute your outgoing mail across multiple API, SMTP Relay, or MTA delivery policies based on percentage allocation and warmup status.
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\*Delivery is when a message is successfully delivered, Deliverability is when the message hits the inbox.
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**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.
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<div align="left"><figure><img src="/files/fDBUlMe2E7zIHNmEnAc8" alt="" width="375"><figcaption></figcaption></figure></div>

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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.&#x20;
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<figure><img src="/files/imEvJQMs7VeQyl959FAU" alt=""><figcaption></figcaption></figure>

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

<figure><img src="/files/C3tjsNNNIAPfqfzBp8i4" alt=""><figcaption></figcaption></figure>

Use the dropdown to select a [domain group](/docs/advanced-postal-route-configuration/contact-list-domain-routing.md) you've created previously.

<figure><img src="/files/N2H4KS0mRAnGTBfmIkzi" alt=""><figcaption></figcaption></figure>

Select an alternative path for delivering mail to this domain.

<figure><img src="/files/fkIcBLEpqg97nYihJlGc" alt=""><figcaption></figcaption></figure>

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

<figure><img src="/files/nEsibWH8hZcHwmxaNtZh" alt=""><figcaption></figcaption></figure>

Use **partitioning** to split your email for the *same* domain group across multiple email service providers or MTA delivery policies.&#x20;

<figure><img src="/files/4FhVMfUiSy0UVzFtCmme" alt=""><figcaption></figcaption></figure>

<figure><img src="/files/NgBBk4GWJ0x1nJRs1Ka6" alt=""><figcaption></figcaption></figure>