Sending the same email to multiple users

A feature in our application allows us to send emails from the application itself.

Currently, the UI is nothing complex, it's just a form with a "to", "subject" fields, and a body. The "to" field is also able to currently accommodate multiple email addresses.

When the users receive this email, they will of course see all the other email addresses that the email was sent to.

For privacy purposes and just a general preference by some of our users in general (this is a legal sector so privacy is important), the emails must sometimes be sent individually - even though they'll all have the same subject/body.

What is the most efficient way for our staff to send out these emails?

I've thought about the following approaches:

(A) Allow the user to append additional "to" fields every time they click on the "+Add" button.

PROS:

• Straightforward

CONS:

• Our staff sometimes needs to copy/paste email addresses in bulk so they would have to individually copy/paste each email into its own "to" field
• The current "to" field is able to accommodate multiple emails. If you append a new "to" field, does that mean each "to" field will still be able to accommodate multiple emails?

(B) Add a checkbox for "Send as separate emails" which means the emails will be sent out individually.

PROS:

• Efficiency - a lot of times, our staff has to copy/paste email addresses in bulk, so to have a one-click solution to be able to send individual emails is a time-saver!

CONS:

• Our staff might accidentally miss clicking this button, hence, will result in recipients being able to see other people's emails.