I get quite a few e-mails from onliners who can’t stand “top posters.” Top posting is the practice of hitting the Reply button and just typing away.
The problem with this bad habit is that you tend to not address items point-by-point as the Sender would prefer. More times than not issues are left open thereby causing a second unnecessary e-mail from the Sender to ask again. Or, the Sender is not sure as to what parts of their e-mail your comments may apply. Thereby, once again, causing the Sender to send another e-mail to get clarification.
This can all be avoided by properly down-editing your e-mails and responding point-by-point. This extra effort is worth the time taken to avoid misunderstandings and having to create additional e-mails that could have easily been resolved in one fell swoop.
Yes, there will be those e-mails that can be replied to thoroughly by top posting a reply. However, be sure to include a greeting as well as a courteous closing when doing so. To just hit Reply and type your comments without a greeting and closing can cause you to appear lazy and/or terse.
And as usually is the case, I have an article on the considerations of down-editing for you review: How to Down-edit Your E-mail.