If you have an important point to make in an e-mail, it is a good idea to use all capital letters.
Using all capital letters is seen as poor e-mail netiquette because it makes it look like you are shouting.

Question

Quizplus · Accepted Answer

Using all capital letters in an email is generally considered poor etiquette because it can be interpreted as shouting or expressing anger, making it inappropriate for emphasizing important points in a professional or respectful manner.

If You Have an Important Point to Make in an E-Mail