How can you query on nested key value pairs?

How can I query in Loki/Promtail a nested key value pair like this one:

[{"action":"allowed","reason":"","reason_extra":"","delivered":"delivered","delivery_detail":"mail.domain.com:25:250 2.0.0 Ok: queued as 6F/89-18578-5391D421","email":"luser52@domain.com","taxonomy":"none"}]

…or do I need to parse this in the promtail config pipeline stage?