Just joined this year
I basically cc'd a customer into an email chain where a bunch of client employees were discussing how to best help the customer
Then some lady from the client complained to my manager and said I shouldn't have
She also said me emailing a pair of managers 'To whom it may concern' sounded frosty and unprofessional (?)
I used 'to whom it may concern' bc my email was addressing a bunch of people in senior positions and I thought it was more professional than going 'Dear X, Dear Y, Dear Z, Dear A' or 'Hi all'
My manager told me that essentially the lady felt annoyed that I gave this client problem without trying to sum up the problem myself and present her with some action points and her complaints re the To whom it may concern email were to do being put off by the massive problem I gave her re the client