Key point: no difference btwn email offer letter and signed pape

no difference btwn email offer letter and signed paper letter, as long as the content is the same

so no need to hang up just because it's emailed offer letter, as long as the email came from someone who has legal authority to represent the hiring institute (such as HR - preferred, director, hiring manager, but normally it's HR; so janitor/chef/coworker does not count  )