On your latter worry, it seems like there's some of that with earlier eras' figures as well. For example, some people's opinion of Simone de Beauvoir and Jean-Paul Sartre has shifted for the worse since their correspondence was published, since much of it is more like a sordid chatroom log, full of offhanded gossip about other people and such, than like the philosophical works they intended for public consumption.
Indeed we all have a common blithe ability to write a rotten sentence. But if you look at, say, jwz's broad swatches of data, or some other such figure, you can see that the bad emails are par for the course. I'd be worried if the figures of the 21st Century couldn't write an e-mail, at any position of the scale of troll to hero.
a) You can be intentional about all your public writing - and I think that we have learned by now that email always has the potential to become public.
b) You can set up a delay-sending rule in your email client so that you have a grace period between pressing send and the message actually being sent - this has saved me embarrassment on any number of occasions.