What are the five rules of email etiquette? 15 Email Etiquette Rules Every Professional Should Follow. ... Include a clear, direct subject line. ... Use a professional email address. ... Think twice before hitting "Reply all." ... Include a signature block. ... Use professional salutations. ... Use exclamation points sparingly. ... Be cautious with humor.What are the do's and don'ts of email etiquette? The Do's and Don'ts of Email Etiquette Do have a clear subject line. ... Don't forget your signature. ... Do use a professional salutation. ... Don't use humor. ... Do proofread your message. ... Don't assume the recipient knows what you are talking about. ... Do reply to all emails. ... Don't shoot from the lip.