Messages are conveyed through channels, with verbal, including face-to-face meetings, telephone and videoconferencing; and written including letters, emails, memos, and reports.
Different channels have different strengths and weaknesses. For example, it’s not particularly effective to give a long list of directions verbally, while you’ll quickly cause problems if you criticize someone strongly by email. Therefore, it is very important that you send your intended message through a proper channel.