Using bcc does NOT necessarily mean to spam users.
In my case I need to notify 100 user - let's say - of a wall activity
that they agreed to received by email but I don't want to use `to:` as
it will disclose their email to each other. And I don't want to send
individual email either because all the benefit of the Mailchimp's
queue buffer will be lost as I will send all the 100 messages in
series which approximately will take 0.6 seconds * 100 = 60 seconds.
This notification are not a campaign as they are generated on fly as
the events happened.
If Mailchimp doesn't allow using bcc: sooner I will be forced to call
Amazon SES directly as they volume of email will grow.