Different types in part 2
AN ARTICLE is usually written for an English-language magazine or newsletter, and the reader is assumed to have similar interests to the writer. The main purpose is to interest and engage the reader, so there should be some opinion or comment.
AN EMAIL/A LETTER is written in response to the situation outlined in the question. Letters and emails in the Cambridge English: First Writing paper will require a response which is consistently appropriate in register and tone for the specified target reader. Candidates can expect to be asked to write letters or emails to, for example, an English-speaking friend or colleague, a potential employer, a college principal or a magazine editor.