I make large use of the e-mail, and I appreciate what I would call the lightness and lack of engagement it inplies: It’s good for ASD people who are often scared of any type of engagement with people. E-mail moreover is often used with people you don’t know personally. This further reduces any kind of engagement: I rarely use e-mail with people I know if not for pratical businesses (appointements etc.). Still I have some reservations about it.
The lack of responsibility it allows may also be negative. In “The Human Stain” by Philip Roth the tragedy is triggered by a charge delivered by a female student against the main character. The student writes the accusation in an e-mail. She is a little uncertan if to send the mail or not. At last, “yes, no, yes, no” she pushes the button “send”. And the tragedy develops. If she had to write the accusation in a real letter, buy a stamp and go to look for postal box, it’s not sure the whole thing would happen.
And the why “Hi” and not “dear” as in a normal letter? There is a little more freedom in the closure, which may even contain a hug, though normally the end is the colorless“ best wishes” or nothing at all.
I also deprecate the habit of nor erasing the addressee letter, so that sometimes an e-mail may be long some miles of exchanges.