You might mention which version of Seamonkey you have installed for Windows 8.1. Too bad the one person here at VideoHelp who I know uses Seamonkey is a Windows 8.x hater likely to tell you you should never, ever use Windows 8.x for anything. LOL.
I never tried Seamonkey, so I'll be of little help. I don't even use email software on a PC anymore since I do my email through free services with no ability to transfer email to a PC.