input fields – Best practices for validating emails in a text box

I want to allow my users to add recipients to a text address in a text box by simply writing their address manually or by copying and pasting them somewhere. Email addresses are separated by a comma or a new line.

How to validate an email address?

If it is an incorrect address, say, john.doe@example.com, how do you tell the user that it is incorrect?

If it's an incorrect address, say, john.doe @ example, com, how do you tell the user that this is incorrect?

A) Show them a notification in the text box?

If you have several errors, you can always expand the notification below and scroll through it.
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B) Offer a tip / notification?

This option would be very frustrating when the user makes several mistakes.
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C) Do you offer a validation?

As I understand it, the validation of e-mails is not 100% accurate, whatever you do – you can never have any critical cases thought. You may create a nuisance if you do not validate a legitimate email.