When people are getting emotional in an email thread or chat conversation, they tend to express their feeling by writing with Caps Lock on.
Using Caps Lock is similar to shouting to another person. And if you start using Caps Lock it will only make things worse.
If you need to get something done, rather use words like ‘important’ or ‘urgent’ in your subject line. If there is a need to highlight certain parts of your email, you can make them bold or italic.