# Sendable, filtered and random data extensions

*Marketing Cloud Engagement Developer Study Guide · Data Modeling · Last updated November 3, 2026 · https://www.certifyforce.com/study-guide/marketing-cloud-engagement-developer/data-modeling/sendable-filtered-and-random-data-extensions*

Standard, filtered and random data extensions, sendable versus reference tables and the send relationship, field and primary key rules, external keys, retention policies, and the data extensions that send logging and Data 360 create.

- Certification: Salesforce Marketing Cloud Engagement Developer
- Exam section: Data Modeling
- Study guide: https://www.certifyforce.com/study-guide/marketing-cloud-engagement-developer

**Official exam objective:**

> Given a scenario, differentiate the various types and uses of data extensions in Marketing Cloud.

## What the exam expects

- Choose between a standard, filtered or random data extension, and between a sendable table and non-sendable reference data, from a requirement.
- Configure a send relationship and pick field data types and primary keys that the platform accepts.
- Decide when a data extension beats an Email Studio list for an integration.
- Explain what the name, external key and Type properties do, and what a developer can change.
- Apply a data retention policy and know when it can't be added retroactively; recognize the data extensions that send logging and Data 360 activation create.
- Key terms: **sendable data extension** (a table whose send relationship maps a field to the subscriber); **filtered data extension** (a segment of an existing data extension); **random data extension** (a random split of a source); **external key** (the unique identifier API calls use).

## Key facts

| Fact | Detail | Source |
|---|---|---|
| Types | Standard, filtered or random; Type is set by the application | [Data Extension Properties](https://help.salesforce.com/s/articleView?id=mktg.mc_es_de_properties.htm&language=en_US&type=5) |
| Subscriber key relationship | Only Text, Email Address or Phone fields | [Data Extension Properties](https://help.salesforce.com/s/articleView?id=mktg.mc_es_de_properties.htm&language=en_US&type=5) |
| Field names | Alphanumerics, spaces, dashes, underscores and periods only | [Create a Data Extension](https://help.salesforce.com/s/articleView?id=mktg.mc_es_create_data_extension.htm&type=5&language=en_US) |
| Primary keys | Unique, up to 850 characters, can't be modified after creation | [Create a Data Extension](https://help.salesforce.com/s/articleView?id=mktg.mc_es_create_data_extension.htm&type=5&language=en_US) |
| Random splits | Up to 12 at a time | [Random Data Extensions](https://help.salesforce.com/s/articleView?id=mktg.mc_es_create_random_de.htm&type=5&language=en_US) |
| Filtered data extension | Sendability follows the source; refresh to pick up new records | [Create a Filtered Data Extension](https://help.salesforce.com/s/articleView?id=mktg.mc_es_create_filtered_de.htm&type=5&language=en_US) |
| Retroactive retention | Best practices: not above 100 million records; retention article: row-based under 1 billion | [Contact Delete Best Practices](https://help.salesforce.com/s/articleView?id=mktg.mc_cab_best_practices.htm&type=5&language=en_US), [Data Retention Information](https://help.salesforce.com/s/articleView?id=000387245&language=en_US&type=1) |
| Data 360 audiences | Sendable data extensions in the Shared Data Extension folder | [Data Extensions for Data 360](https://help.salesforce.com/s/articleView?id=mktg.mc_cab_c360a_data_extensions.htm&type=5&language=en_US) |

## Check yourself

- When is Reset period on import unavailable for a retention policy?
- How many groups can one random data extension build create?
- Why must a Data 360 audience's personalization strings be checked after activation?

## Sources

- [Data Extension Properties for Marketing Cloud Engagement](https://help.salesforce.com/s/articleView?id=mktg.mc_es_de_properties.htm&language=en_US&type=5)
- [Create a Data Extension in Email Studio](https://help.salesforce.com/s/articleView?id=mktg.mc_es_create_data_extension.htm&type=5&language=en_US)
- [Email Studio List vs. Email Studio Data Extension](https://help.salesforce.com/s/articleView?id=mktg.mc_es_list_versus_data_extension.htm&type=5&language=en_US)
- [Learn About Data Extensions (Trailhead)](https://trailhead.salesforce.com/content/learn/modules/marketing-cloud-contact-management/learn-about-data-extensions)
- [Data Extensions with Enhanced Subscriber Features](https://help.salesforce.com/s/articleView?id=mktg.mc_es_de_enhanced_subscriber.htm&type=5&language=en_US)
- [Create a Filtered Data Extension](https://help.salesforce.com/s/articleView?id=mktg.mc_es_create_filtered_de.htm&type=5&language=en_US)
- [Create a Data Extension That Contains Randomly Selected Subscribers](https://help.salesforce.com/s/articleView?id=mktg.mc_es_create_random_de.htm&type=5&language=en_US)
- [Data Extensions in Contact Builder](https://help.salesforce.com/s/articleView?id=mktg.mc_cab_data_extensions.htm&type=5&language=en_US)
- [Enable and Modify Data Extension Retention Policies](https://help.salesforce.com/s/articleView?id=mktg.mc_cab_manage_data_retention_policy.htm&type=5&language=en_US)
- [Contact Delete Best Practices in Contact Builder](https://help.salesforce.com/s/articleView?id=mktg.mc_cab_best_practices.htm&type=5&language=en_US)
- [Data Retention Information for Marketing Cloud Engagement](https://help.salesforce.com/s/articleView?id=000387245&language=en_US&type=1)
- [Data Extensions for Data 360](https://help.salesforce.com/s/articleView?id=mktg.mc_cab_c360a_data_extensions.htm&type=5&language=en_US)
- [Create an Email Send Logging Data Extension](https://help.salesforce.com/s/articleView?id=mktg.mc_cab_create_an_email_send_logging_data_extension.htm&type=5&language=en_US)

## About the full unit

The "Core concepts", "Exam traps" and "Worked scenario" sections of this unit, its 12 linked practice questions, and unlimited timed mock exams are included with the Marketing Cloud Engagement Developer pack (USD $19): https://www.certifyforce.com/practice-exams