Writing anything is a delicate and often fraught journey that deviates from the route you've planned out in your head, going off road into thorny scrubland of politics and power.
In a study published in the journal Social Cognitive and Affective Neuroscience in 2014, a group of researchers confirmed that feeling understood activates bits of the brain which are associated with reward while not feeling understood sets off parts associated with negative affect.
It is hard to know the mood of the other person solely through their text, but it is important to infer it. It's possible to get it wrong in person, but we are really attuned to doing this. Some of us more than others, but most adults are able to read social cues intuitively.