save an email in a folder
If you use Thunderbird as your mail program, here is some useful information for saving a single mail as a file on your computer. There are two methods, the first (for the more skilled with the mouse) shows how “drag” an email “out” of the mailbox mail, directly in the Desktop of your PC/SERVER, the second is the “Save as...”.
Once you have located the email, “grab” it by holding down the left mouse button on it. Drag it out of Thunderbird and then release the button.
The file will be created with the name of the subject of the email being dragged.