There is no "4th rule" of email etiquette that is widely accepted or recognized. However, there are many additional principles of email etiquette that are important to follow when communicating through email, including:
Use a clear, professional subject line:
Show your recipient what the email will cover in a clear and concise subject line. This will help them decide whether to open your email and prioritize their inbox.
Proofread every email you send:
Make sure there are no grammatical or professional errors in your emails. This includes spelling the recipient's name correctly and using simple sentence structures, correct capitalization, and punctuation.
Write your email before entering the recipient's email address:
This will help prevent you from accidentally sending the message too early.
Double-check that you have the correct recipient:
There is nothing worse than sending an email to the wrong person or a confidential document to the wrong client or company.
Ensure that you CC all relevant recipients:
It is unprofessional to leave out a colleague or client from a relevant email chain. Be mindful of who should be informed about a given matter and include them in the CC list.
You don't always have to "reply all":
Think about who needs to read your response and avoid clogging up their inbox with emails that are not relevant to them.
Reply to your emails:
Acknowledging that you received an email, even if you can't respond right away, is good etiquette. It shows that you are professional and respectful of the sender's time.
Include a signature block:
This includes your full name, title, company, and contact information. It helps the recipient understand who you are and adds credibility to your email.
Use the appropriate level of formality:
Depending on the recipient and the purpose of the email, you may need to use a more formal tone. Use proper greetings and closings, such as "Dear," "Sincerely," and "Thank you," and be sure to use "please" and "thank you" where appropriate.
Keep emails brief and to the point:
No one wants to read a long, rambling email. Be concise and get to the point quickly, and follow up with a phone call or additional email if necessary.