In literary Ukrainian, when you use чи, you normally move the main verb to the beginning of the sentence: Чи шукаєте ви пошту?
Чи Ви шукаєте пошту could be understood 'Is it you who are looking for the post office?'
Yeah... It's not a common sentence to say. Nevertheless, it's grammatically correct and can be meaningful given a context. E.g. "How do you send a letter? - You drop it into a mailbox. - And how do you find a mailbox? Do you look for a post office? Or are there mailboxes in other places?"
So, now it's accepted.