Email is best for informal, internal communication while memos are more formal. If the communication could seriously impact the recipient, public, or company, a formal memo is preferable. Memos include identifying information like recipient, author, date and subject at the top, with the main point at the beginning of the content and a concluding paragraph. Emails focus on a concise subject line, recipient, message body, and signature with or without attachments. Both emails and memos should be concise and avoid long-windedness, stating the reason for writing up front.