See two screenshots below.

We pass an array of email addresses relevant to an event as an event attribute called event.user_emails and we use the following liquid logic to pass this array as a string of comma separated email addresses to bcc mass send notifications to the relevant users for the event.

I’ve verified that this passes the validation checks about events being properly set up.

However, when the email gets attempted to send, i get the following issue/attempted status:
invalid (mail: expected single address, got “@glencoco.io”

even though it is passing through a comma separated string of email addresses. 

Are there limits to how many user emails can be added to bcc’s in customer.io?

Is there an alternative way of implementing this?