Custom identifiers, or custom IDs, let you add your own identifiers to your Marketing account. You can use them to create, retrieve, update, and delete contacts, in the same way as the system identifiers. Custom IDs help you track the same person across all the systems you store data in, and bring together data from several sources.
Learn more in Create custom identifiers.
System identifiers
By default, Marketing has three system identifiers:
Contact ID
A numeric identifier that Marketing assigns to each contact when you create them.Email
The contact's email address.Mobile number
The contact's mobile number.
Custom identifiers
A custom ID is different from the Contact ID. Marketing assigns the Contact ID automatically; you create and manage your own custom IDs.
Custom IDs sit alongside the system identifiers. For example, you might create a custom ID for:
a CRM ID
a shopper number
a profile ID
A contact can have several custom IDs, but only one email address and one mobile number.
Custom ID or a data field?
Choose a custom ID when you need to identify or look up a contact by that value - through the API or an import, for example, a custom ID works the same way as an email address or mobile number.
Choose a data field when you only need to store information about a contact, without using it to identify them. Unlike a data field, each custom ID value must be unique to one contact, and custom IDs aren't currently supported in the segment builder.
Where you can use custom IDs
Where | Status |
Segment rules (as a filter condition) | Not supported in the segment builder. Use the Contacts and Insight data API services instead. |
Forms | A hidden value block can't write to a custom ID, and a custom ID can't be a public-facing form field. |
Programs | The Update contact node doesn't support custom IDs. |
Sending | A custom ID can't be used as a send address. |
Ecommerce and CRM connectors | See Custom IDs in ecommerce and CRM connectors below. |
Rules and limits
Rule | Details |
Custom IDs per account | Up to 10. There's no limit to the number of contacts that can have a value for a custom ID. |
Name length | Up to 50 characters. |
Name characters | Letters, numbers, hyphens or dashes, and underscores only. |
Name clashes | A custom ID can't have the same name as an existing custom contact data field. |
Value length | Up to 256 characters. |
Unique values | Each value must be unique to one contact within that custom ID. For example, two contacts can't have the same CRM_ID value. Email addresses and mobile numbers must also be unique. |
Contacts need an email address or mobile number | You can't create a contact that's identified only by a custom ID. Each contact must also have an email address, a mobile number, or both. |
File imports | You can't overwrite an existing custom ID value with a file import. |
Deleting a custom ID | Deletes all of its values for every contact. This is permanent, and you can't recover the values from the recycle bin. |
Custom IDs in ecommerce and CRM connectors
Our ecommerce and CRM connectors don't support custom IDs yet. We're working on support for them. To share feedback or use cases, contact your Customer Success representative.