The structure of folders (tags) emails.

Greetings
I am already very concerned about the problem of creating the optimal structure for the distribution of emails.
Each time, the structure I create either grows to unrealistic sizes and becomes incomprehensible, or it is very simple and makes it difficult to find the right letter (imagine that there is no search by letters :)).

Actually, I would like to learn from the respected habraradi how they cope with the large flow of letters, how they structure mail, so that it is convenient to search for the right letters.

Thank.