You must had experience it before. When you have to send a chat or message to someone who does not really know you. Or it might be the first time you send a message to them.
Many of us use a super polite language when the first time we send a chat, especially to a lecture. However, some of us might does not really pay attention to these things, sometimes we might did not say the greetings and even using to many abbreviations.
In my case, I did chat my friends, my family, and my lecturers. However, I implemented some different ways for them. I will use many slang words and abbreviations while chatting with my friends and my brother. But, I would not use abbreviations and slang words to my lecturer. I tend to use more formal language to them, because it is not polite. Furthermore, lecturer is someone who is older than us.
But, there are some lectures who do not really pay attention to the formal language. So, I will try to speak more comfortable but still in a manner full way. Here, I am trying to act more friendly but still in the right positioning. The reason why I doing so is to make both of us comfortable in the conversation. I do not want to be considered as too rigid or stiff.
Based on the case above, I will see the respond from the others. Usually after several chats I will try to use more comfortable language rather than but still in a polite way of speaking. Because while you doing a chat, you are not in a face to face position with your opponent. They read your message based on their intonation and if you write something which is unclear for your opponent, they might misunderstood your message. Therefore, the use of formal and informal language should be applied on a certain conditions.