Email(s) can be copied to a different folder using Rainmail Webmail as follows:

1. Select the Email(s) to copy. Multiple emails can be selected by using Shift / Ctrl key while selecting.
2. Right click on the selected emails. That will bring up the following menu

3. Click on Copy email to... menu (indicated by Red Oval above). That will bring up the following dialog

4. Select the folder to copy to, from the displayed list of folders. Click on OK.
5. The emails will be copied to destination folder.