# properties.email.description
Account email — receives the verification link.

# properties.ref.description
Referral code of the account that referred this signup, when any.

# properties.channel.description
Distribution-channel slug the signup came through (e.g. wordpress-plugin) — the where to ref's who. Invalid values are dropped, never an error.

# properties.referrer.description
First-touch landing referrer URL (external document.referrer captured on first visit). Invalid values are dropped, never an error.