Why do people (myself often included) feel the need to make excuses or ask forgiveness for our e-mails? If I take a day or two to reply, or if my message is short, what is there to forgive? Would an immediate, hair-trigger response really be preferable? Would twice as many words really do a better job of conveying my message?
I think the answer is No.
No, a faster response is not necessarily better. No, a longer response is not necessarily better. No, I don't need to apologize for taking time to consider my words, for saying my piece in something shorter than a lengthy epistle, for doing the work I have that is not reading and replying to e-mail. And I certainly don't need to append such an apology to every message I send.
: to a non-urgent matter