Bcc mailed to all means

A classic!

When you see "Bcc" (Blind Carbon Copy) in an email, it means that the email is being sent to a list of recipients, but their email addresses are not visible to each other.

In other words, when you use the "Bcc" field in an email, the recipient list is not visible to the other recipients. Each recipient only sees the sender's email address and their own email address.

This is useful when you want to send an email to a large number of people, but you don't want them to see each other's email addresses. For example, if you're sending a company-wide announcement, you might use the "Bcc" field to keep the recipient list private.

So, when you see "Bcc mailed to all", it means that the email was sent to a large number of recipients, but their email addresses are not visible to each other.