We commonly communicate by means of emails or by sending texts on mobile phones and other small devices. This type of communication is normally informal, and the messages are often written very quickly.
We can write email messages like formal letters, but they are usually informal and involve shortened words and phrases. They often have ellipsis:
Hi, Jim. Just to say, I’m going to be late for the meeting tomorrow but will send the report to you before the end of today.
(Hi = informal version of dear; Just to say = ellipsis of I just want to say/I’m just writing to say; will send = I will send)
Text messages are even more informal and can involve a lot of abbreviations:
[Typical text message]
Sara will b l8 4 the party 2nite. F, xx (Sara, [I] will be late for the party tonight. Francis)