Sent an email - which was meant for the two clients - forgot to Blind CC them resulting in them being able to see each others email addresses. We are all working on the project together/have met and the email was for both of them, I know I should have done them separately and I have reported to data protection colleague whose sent it to the correct channels - I feel so stupid and unprofessional, I have never been shown how to blind CC as I usually just sent separate emails but didn't even think as we are all on the same project :(