我正在使用 go 發送郵件雜志，我嘗試使用 sendgrid 我嘗試了https://github.com/sendgrid/sendgrid-go中的示例 在 main() 上運行一切正常示例代碼如下package mainimport (    "fmt"    "log"    "os"    "github.com/sendgrid/sendgrid-go"    "github.com/sendgrid/sendgrid-go/helpers/mail")func main() {    from := mail.NewEmail("Example User", "[email protected]")    subject := "Sending with Twilio SendGrid is Fun"    to := mail.NewEmail("Example User", "[email protected]")    plainTextContent := "and easy to do anywhere, even with Go"    htmlContent := "<strong>and easy to do anywhere, even with Go</strong>"    message := mail.NewSingleEmail(from, subject, to, plainTextContent, htmlContent)    client := sendgrid.NewSendClient(os.Getenv("SENDGRID_API_KEY"))    response, err := client.Send(message)    if err != nil {        log.Println(err)    } else {        fmt.Println(response.StatusCode)        fmt.Println(response.Body)        fmt.Println(response.Headers)    }}但我需要將 HTML 文本發送到郵件雜志所以我需要修改htmlContent := "<strong>and easy to do anywhere, even with Go</strong>"到htmlContent := "<div>some thing I want to send</div>"所以我做了以下事情func content() string {    return fmt.Sprint(`<div>many many html here</div>`)}func main() {    key := "my key of sendgrid"    send(key)}func send(key string){    from := mail.NewEmail("Example User", "[email protected]")    subject := "Sending with Twilio SendGrid is Fun"    to := mail.NewEmail("Example User", "[email protected]")    plainTextContent := "and easy to do anywhere, even with Go"    htmlContent := content()    message := mail.NewSingleEmail(from, subject, to, plainTextContent, htmlContent)    client := sendgrid.NewSendClient(key)    response, err := client.Send(message)    if err != nil {        fmt.Println("==========send1 failed with",err)    }    fmt.Println("send1 result")    fmt.Println(response.StatusCode)    fmt.Println(response.Body)    fmt.Println(response.Headers)}func main() {    key := "my key here"    send(key)}