Very clear and direct. A+ would vote again

This response makes no distinction between TO and CC. If CC has the exact same responsibilities as TO, then what use is it? Your answer renders CC useless.

@CodeSeeker if your business process depends on your customer knowing and acting on the fine differences between TO and CC, then you have a problem.

@CodeSeeker Whether he was CCd, BCCd, or anything else. He is the sole person in the role, and it was his responsibility. If this response makes no sense to you, I hope your resume is up to date.

I agree with CodeSeeker. Yes, OP should have look more into it altough there's a reason TO and CC aren't the same thing. If I want someone to answer me back or give me a feedback I'm gonna put his name in TO not in CC. What is the purpose of CC then if you should treat it the same as TO? Also OP probably assumed his coworker already answered the mail since the client directly wrote to him. Again OP should probably have double check with his coworker but then again there's a reason why CC exist.OP should just explain himself and I'm pretty sure his boss will see it was simply a misunderstanding

Also, I guess there's no need for the passive-agressive approach here.

@Gainz There is nothing passive about my aggression when people try to shift responsibility. If the client sent in an illegible letter to the office written in crayon, and addressed to the admin instead of the OP, and the OP knew about it, it would STILL be his responsibility, as he is the only one in that role.

@RichardU I do agree with the responsibility thing but here OP didn't even seems aware of the project mentioned in the email he was CC. IMO it is kinda hard to blame it on OP in this situation as being CC isn't the same as TO. IMO the situation as a whole is more of a misunderstanding than a lack of responsibility.

@Gainz I've seen to many people lose their jobs over misunderstandings. The OP wanted to go into the manager's office and make excuses. Trust me, the manager's words would be much harsher than mine and would only make matters worse. I stress the responsibility because that's what management will stress. If the client had walked instead of complaining, the OP would be out of a job.

@RichardU i reread the OP and what’s clear to me is that it was very much not clear that he was supposed to do anything. He knew nothing about the project, the person who did know was in the TO slot, and the email was addressed directly to that person. It should not be a fireable offense or even a real disciplinary one that he just didn’t realize there was something for him to do. If he was supposed to provide support on this project, why was he never told?

@Eigentime I’m pretty sure the customer did know the difference between TO and CC given he addressed only the superior directly in the greeting.

@CodeSeeker it doesn't matter what the client did, it was the OP's responsibility. If I'm in a crosswalk, and a car is not stopping, but about to hit me, I'm going to get out of the way, not argue with physics over the fact that the driver is in the wrong.

@RichardU the core fact is that the OP didn’t realize it was his responsibility, and had a few signals that are a reasonable explanation for that belief. You’re taking such an extreme view of this! I understand the principle, but was no risk of death in this scenario, lol. Glad you’re not my boss, because you’re acting mighty pointy-haired. The business should just clarify what is expected of both employees because the failure of the boss to respond to an email addressed to him about a project he worked on and the other guy didn’t was a key contributing factor to the gap in customer support.

@CodeSeeker Well, the last person I dealt with who was in this position, straightened himself out, stopped being naive, and became known as the most careful, meticulous, and dedicated employee we had. There is nothing PHB about teaching people the skills they need to protect themselves and advance. If I were your boss, you'd probably hate me, but you'd respect me, and benefit from what I could teach you.

@RichardSaysReinstateMonica your assumption I need to be taught something isn’t accurate. It is unlikely I’d make the same mistake as the OP. The issue here is how to handle that mistake. Lightly.

@CodeSeeker if you don't think you need to be taught something, I feel sorry for you, we all have something to teach, and we all have something to learn.

@RichardSaysReinstateMonica you’re acting ridiculous. My statement wasn’t a global one. Your attack of slanted interpretation is inappropriate and unnecessary. I reject YOU as my teacher on THIS topic. Your quickness to characterize and interpret and globalize all doubly confirm that working under you would definitely be a series of amazing lessons... but not the ones you think! :) :)

TO: means the person who the message is intended for, and who is expected to take action. CC: literally comes from "carbon copy", meaning a copy of the message is being sent to another person for their information. These meanings existed long before email. Whether someone is expected to act on a CC would be situational and specific to a policy. There is no automatic assumption that CC implies action to be taken by the CCed user.

@GoodbyeMsChipps Which, I am sure will be great consolation on the unemployment line.

If you get fired for this, your job is in constant jeopardy anyway, best find it out now, rather than when you're fired for wearing blue socks, or going to the bathroom, or liking ABBA.

@GoodbyeMsChipps or, if you're socks are untied. But, that's not the point. The consequences of this one were minor because the client only complained. If they had lost the client, management wouldn't care if it was a "to" or "CC". Management would have two questions: 1) DID YOU KNOW ABOUT IT? and 2)WHY DIDN'T YOU DO ANYTHING? The fact that the damage was minor doesn't change that it could have been major. If you drive drunk, and make it home without killing anyone doesn't change the fact that you drove drunk

Comparing NOT responding to an email to driving drunk means this conversation has degraded to the point where it's meaningless.

@GoodbyeMsChipps No, it's illustrating the concept of "moral luck". If the same action produces two different outcomes, the fact that in one instance, the outcome was fortuitous makes the action no less wrong. In this case, if the client had pushed for the OP to be fired instead of just complaining about being neglected, the outcome would have been just that. But, more to the point. How will my advice to the OP cause any sort of negative consequences?