# Metadata Calls

Mailjet being an all-in-one email solution, we allow you to upload contact properties to personalise the content of your messages, whether that's in the context of a marketing campaign or in a transactional email.

The [`contactmetadata`](/docs/api-reference/email-api/categories/contacts/) resource allows you to define contact properties while the [`contactdata`](/docs/api-reference/email-api/categories/contacts/) let you attach them to a given contact.

Later on you can use them in your emails. Please refer to our [Personalization](/docs/email-api/contact-management/contact-mgmt-overview/#manage-contact-properties) API guide to learn more.