For G Suite.
For Office 365.
When sending one mail to multiple recipients, you will receive the same number of [sent mail] notification mails as that of the recipients.
Is it correct that if there are multiple recipients, the number of [SEND] action you have to execute on the admin page is just one time?
Yes, you are. The number of Notification mails which you will receive is the same as that of the recipients, however, the action you have to execute on the admin page is just one time.