Hi, I just tested the program and saw that this feature is already implemented in the inbox for receivers. Do you mean that you want to implement this feature in the sent section for the sender as well?

I deleted all cache and checked again, so I think it was reversely implemented, it should be:

if (email.read === false) {
  item.style.backgroundColor = '#D3D3D3';
}else{
  item.style.backgroundColor = '#FFFFFF';
}

to display the grey color if an email is unread, otherwise the white color.

And, yes, in the sent mailbox section, it is not working. Any ideas? It should be working for all mailboxes, not only the inbox. Please, feel free to make a pull request.

I think it is not working in the sent mailbox section. I will submit a pull request to fix it.