Honoured to have your first post Benjie. It is open-source and made in Electron, but I'm not sure it's upto much at the moment. I've mostly been working on getting IMAP and SMTP setup as opposed to any graphical work.

If you're interested in helping out, I'd love any help I can get. Email me at the address on my profile page and I can give you some more details. The current design looks as follows:

https://puu.sh/vmtT6/b803a88da5.png