Prioritize your E-Mail Content
If you have a lot of action points to discuss about, try to spread them over a few separate E-Mails. If it is a very long E-Mail, recipients may only read partway and hit "reply" as soon as they have something to contribute. It is quite common for them to forget to keep reading. This is part of human nature. Spreading them over a few E-Mails reduces that risk. Alternatively, you may inform the recipient first up that there a lot of action points and you need them to read through all of them before replying. You may also consider numbering them and presenting them in order of importance.