If you have to write more than two short paragraphs to express your feelings to someone (or especially a client) on something that feels important, pick up the phone and talk to the person.
E-mail is wonderful. But too much tone can get lost… too much room for misinterpretation.
Sure, e-mail is easier.
But talking is much more effective.
(Oh, by the way, I always come back to this rule after crafting a 500 word nuanced reply to someone that I never send.)