Contacts

A contact represents a person in your audience. Contacts have channels (email, phone), custom fields, and belong to lists.

Channels

Each contact can have multiple communication channels:

• Email — for email campaigns and transactional messages
• Phone — for SMS messages

Custom fields

Store additional data on contacts using custom fields. These can be used in template personalization and segment conditions.

Tags

Tags are free-form labels you can attach to contacts (for example vip, newsletter, free-trial). Tags are a special reserved key on each contact's data object — stored as an array of strings — and are used for segmentation and targeting alongside lists and custom fields.

Unlike lists, tags are lightweight: a contact can have any number of tags. You can set the tags on an individual contact via the REST API, or add, remove, and replace tags across many contacts at once via the nitro_manage_audience MCP tool.

Subscription status

Contacts can be subscribed, unsubscribed, or bounced per channel. Unsubscribed contacts are automatically excluded from campaigns.