It’d be extremely difficult to have it work any other way, assuming the recipients are on different email servers.
As soon as you hit ‘send’ a discrete copy of the mail is sent to each recipient(*), it’s just like sending postal mail. If you sent six letters out to your friends and two come back marked Return To Sender, did the other four make it? Of course. Same principle. It’d be pretty complex to send mail in an all-or-nothing manner, either electronically or physically, for broadly similar reasons.
(* – there’s an exception to this; if you’re only sending internal mail, e.g. you’re using work email sending to colleagues on the same email system, Exchange (and presumably other modern mail servers) will keep one central email body that all the recipients can see. So, a company-wide mailout is no more ‘expensive’ on storage than a mail to one user, at least until everyone starts replying anyway. The original answer still holds true though, even if some recipients bounce the others will still get the mail.)