I am very new to Swift programming. But for testing I was able to access the email content with session.composeContext. I did not fully understand the reason. rawData is sometimes empty. import MailKit class ComposeSessionHandler: NSObject, MEComposeSessionHandler {   func mailComposeSessionDidBegin(_ session: MEComposeSession) {     // Perform any setup necessary for handling the compose session. if let data = session.composeContext.originalMessage?.rawData as? Data {       let dataStr = String(data: data, encoding: .utf8)       print(dataStr)            }   } // ... }