Transfer of email files to Desktop using Windows and Thunderbird

I am using a Laptop and a Desktop, both have Windows as OS and I also installed Thunderbird Email client. Both PC’s are configured with the same email. The purpose of the Desktop is to save all emails on server until I delete them. The laptop is set for all emails on server. The problem is not all messages are sent in the desktop. I have seen some messages in the laptop that were not in the desktop. I tried checking emails in the desktop but I did not find the problem. Any help?
