This is the - fast - response I've got from support:
Thank you for reaching out about the behavior of the Send Email action in automations. Due to security changes from Google and Yahoo, our engineers had to make an update to our Send Email messages that modified how email addresses are presented in the To: and CC: columns to remain compliant with these platforms.
Now, the individual recipient of an email will see their own email address in the To: column of the email. Other addresses that were listed under the To: and CC: columns of your automation action will appear to recipients as a list under the CC: element.
The email preview has been updated so that you can select a specific recipient to see what the email will look like to that particular recipient. Your automation's run history will still display the email addresses as expected in the To:, CC:, and BCC: columns. It'll just present the email order differently to email recipients in their inboxes.
We want to assure you that, despite the order of To: and CC: email addresses changing around, email recipients will still receive emails from the Send Email action and will receive the email only once, even though the preview may make it seem like they will receive the email more than once. Please also know that email addresses in the BCC field will never be exposed to any of the folks in the To: and CC: fields. We apologize for the confusion this causes and for any interruptions this may cause your workflow, but appreciate your support with these compliance updates.
