When replying to an E-Mail, some of the E-Mail's input fields are pre-filled:
The sender of the E-Mail and additional recipients of the E-Mail are automatically entered as recipients of the reply E-Mail.
The E-Mail subject is entered in the subject field of the reply E-Mail. The subject is preceded with the text "Re: ".
The E-Mail text is entered in the forwarded E-Mail. Each cited line is marked at the beginning.