> ## Documentation Index
> Fetch the complete documentation index at: https://docs.apollodeploy.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Contacts and custom properties
> Separate recipient identity, profile data, grouping, preferences, and delivery blocks
A contact is a recipient identity inside one Signal project.
Its record combines an email address with profile fields, custom values, segment membership, topic preferences, global unsubscribe state, and customer-visible activity.
## Contact identity
`email` is required and unique within the project.
The public update contract changes first name, last name, phone, global `unsubscribed` state, and property values; it does not replace the contact's email identity.
Create a deliberate replacement contact when the address itself changes.
A create request can also include initial segment references and explicit topic subscriptions.
The response includes the project ID, contact ID, current properties, segment IDs, topic subscription records, and timestamps.
## Keep the state types separate
| State | What it represents |
| --------------------- | ---------------------------------------------------------- |
| Contact profile | Identity and customer attributes |
| Custom property | Project-defined data attached to the contact |
| Segment membership | Explicit static grouping |
| Topic subscription | An explicit `opt_in` or `opt_out` communication preference |
| Global `unsubscribed` | Contact-wide subscription state |
| Suppression | A project delivery fence for the email address |
A contact can continue to exist while its address is suppressed.
Deleting the contact is not equivalent to retaining a delivery block.
## Current custom-property contract
The public API supports property definitions of type `string` and `number`.
A definition uses:
* A project-unique `key` containing letters, numbers, or underscores.
* A maximum key length of 50 characters.
* An immutable type selected at creation.
* An optional fallback value.
Only the fallback value is mutable on the property definition.
Choose a stable key because changing a business label does not create a key-renaming operation.
Contact property values are submitted as string key/value pairs and validated against the project's definitions.
A fallback is returned or used only where the product contract says the contact lacks an explicit value; it must not invent consent or eligibility.
## Activity and derived evidence
The contact activity endpoint combines recent email events, contact creation, segment changes, topic subscription changes, and suppression changes, ordered newest first.
Engagement and recorded email-validation results are separate derived signals.
Neither overrides consent or suppression.
Do not use a profile field, segment, or engagement score as a substitute for an explicit topic preference or delivery suppression.
Review contact profile, activity, engagement, validation, and deletion behavior.