It's easy to argue that the high speed of modern communications makes it too easy to send an angry reply without considering its impact. But the basic rule is simpler: you shouldn't respond in an angry fashion, whatever the medium.
BBC Point Of View columnist Lisa Jardine uses the example of an angry letter Virginia Woolf planned to send to a correspondent. After thinking better of it, she drafted a more conciliatory reply. Jardine argues that this demonstrates a flexibility inherent in the printed word which doesn't necessarily apply to email:
Woolf - using established letter-writing conventions - takes advantage of the time lapses between exchanges to recuperate, clarify, recast and take control of the argument. The result has the elegance of a formal dance - a kind of minuet, in which the participants advance and retreat according to well-understood rules, until they have arrived at a satisfactory outcome. How unlike the rapid firing off and counter-fire of email messages in which many of us find ourselves engaged nowadays as our predominant means of communicating with colleagues and friends, and even with complete strangers.
However, Jardine then goes on to note that Woolf was frequently guilty of sending inflammatory correspondence, and that ultimately a hasty response is a hasty response in any setting:
No doubt I am sentimentalising the orderliness of written letters by comparison with emails. When feelings run high, an ill-judged letter can cause as much emotional damage as any dashed-off online posting.
And that's the big lesson. Any communication in anger -- whether email, phone or letter -- is likely to create more problems than it solves. Pause, reflect, and work out what problem you're actually trying to solve before responding.
Mourning the loss of the written word [BBC News]