You comment was dead, I vouched for it as it's a valid assumption that you have to notice users on breach. But in this case, it seems like the following applies (34.3.A from your link):
> The communication to the data subject referred to in paragraph 1 shall not be required if any of the following conditions are met:
> the controller has implemented appropriate technical and organisational protection measures, and those measures were applied to the personal data affected by the personal data breach, in particular those that render the personal data unintelligible to any person who is not authorised to access it, such as encryption;
With emphasis on the "in particular those that render the personal data unintelligible". Since the email is no longer an email, it should not be counted as personal data, it's just random characters, and no notification needed.
> The communication to the data subject referred to in paragraph 1 shall not be required if any of the following conditions are met:
> the controller has implemented appropriate technical and organisational protection measures, and those measures were applied to the personal data affected by the personal data breach, in particular those that render the personal data unintelligible to any person who is not authorised to access it, such as encryption;
With emphasis on the "in particular those that render the personal data unintelligible". Since the email is no longer an email, it should not be counted as personal data, it's just random characters, and no notification needed.
IANAL, but that's how I understand it.