为什么WKWebView通过缩放来加载内容HTML？

Question

我在我的项目中使用库mailcore2（http://libmailcore.com/api/objc/index.html）。我想在WKWebView中呈现消息（电子邮件）的主体。当我呈现HTML消息正文时，webView通过将内容HTML缩小得太多来加载内容HTML。我该如何解决？是由于消息的内容吗？还是呈现邮件正文HTML的方法？现在，我仅使用库mailcore2的MCOIMAPSession类实现了IMAP协议。谢谢

屏幕截图：https://i.ibb.co/pb1xG0R/IMG-CA104358-B976-1.jpg

我执行以下操作：

var imapsession: MCOIMAPSession?

func getBodyOfEmail(message: MCOMessage, folder: String, completion: @escaping(String)->()) {
        if mailProtocol == "IMAP" {
            let op = self.imapsession!.htmlBodyRenderingOperation(with: message.imapMessage!, folder: folder)

            print("IMAPSESSION: RENDERING \(message.uid) FOLDER \(folder)")

            op?.start({ (body, error) in
                if let error = error {
                    print("IMAPSESSION: ERROR \(error) HTML BODY RENDERING")
                    completion("")
                } else {
                    if let body = body {
                        completion(body)
                    } else {
                        print("IMAPSESSION: ERROR HTML BODY RENDERING")
                        completion("")
                    }
                }
            })
}

MCOSession.shared.getBodyOfEmail(message: email, folder: folder) { (body) in
                print("BODY: \(body)")
                self.webView.loadHTMLString(body, baseURL: nil)
            }

class MCOMessage {

    var mailProtocol: String // IMAP or POP

    var imapMessage: MCOIMAPMessage?
    var popMessage: MCOPOPMessageInfo?

    var uid: UInt32
    var sequenceNumber: UInt32
    var flags: MCOMessageFlag

    var header: MCOMessageHeader

    var plainText: String?

    // I have only implemented the imap protocol
    init(mailProtocol: String, message: MCOIMAPMessage) {
        self.mailProtocol = mailProtocol
        self.imapMessage = message

        self.uid = message.uid
        self.sequenceNumber = message.sequenceNumber
        self.flags = message.flags
        self.header = message.header
    }

}