How get mail content using Postal Swift Framework

Question

I'm using the Postal is a swift framework providing simple access to common email providers. I have seen demo about it, but I don't know how I can have my text content that I need from a FetchResult? Thanks. This code fetch mail from mail server:

self.postal.connect(timeout: Postal.defaultTimeout) { (result) in
        switch result {
        case .Success():
            self.postal.fetchLast("INBOX", last: UInt(number), flags: flags, onMessage: { (message) in
                message.body?.allParts.flatMap({ (singlePart) -> String? in
                    let textMail = String.init(data: (singlePart.data?.rawData)!, encoding: NSUTF8StringEncoding)
                    print(textMail)
                    return textMail
                })

                }, onComplete: { (error) in
                    if let error = error {
                        print(error)
                    }else {

                    }
            })
            break
        case .Failure(let error):
            print(error)
        }
    }

and result log: Optional("\u{1B}$B$3$N%\"%W%j$O!\"0lEY\u{1B}(BiBeacon\u{1B}$B$r