Hy,

You point out a limitation of the mailing usability in Odoo. On a side, it's normal to have a mail for each destination, just think about spam limitation if the number is too long.

My point s that it should be executed in a batch and a mail should be sent to the sender so that he will be informed of the success of the process.

So it could be a specific development and/or an improvment inquiry

Additionnaly, I found this : https://www.odoo.com/apps/modules/8.0/asynchronous_batch_mailings/ could help maybe