Zoho Projects not accepting emails when using email while on BCC

I was wondering, is there reason why Project Email aliases do not work if they are copied into the BCC of those emails.

One thing we do is send a status update to our (external) customers who most of the time do not have access to Zoho Project.

I want to have these emails added to the forums of ZOHO Project, but I do not want to add the Project Forum email alias to the To or CC fields, as the customer will get a bounce email when he sends a reply-all.

And as I said, I don't want to add the customer to the project in many cases.

Is there a way around this (other than sending the email separately to Zoho - which I also don't like doing)?

Thanks,

Menno