[Fix-5032][Alert]Support email multiple format (#5033)

* support multilple email format

Co-authored-by: 李巨丰 <lijf@2345.com>

dolphinscheduler-alert-plugin/dolphinscheduler-alert-email/src/main/java/org/apache/dolphinscheduler/plugin/alert/email/MailSender.java

@@ -39,6 +39,8 @@ import java.util.List;
 import java.util.Map;
 import java.util.Properties;
 
+import javax.activation.CommandMap;
+import javax.activation.MailcapCommandMap;
 import javax.mail.Authenticator;
 import javax.mail.Message;
 import javax.mail.MessagingException;
@@ -284,6 +286,15 @@ public class MailSender {
      * @return the new Session
      */
     private Session getSession() {
+        // support multilple email format
+        MailcapCommandMap mc = (MailcapCommandMap) CommandMap.getDefaultCommandMap();
+        mc.addMailcap("text/html;; x-java-content-handler=com.sun.mail.handlers.text_html");
+        mc.addMailcap("text/xml;; x-java-content-handler=com.sun.mail.handlers.text_xml");
+        mc.addMailcap("text/plain;; x-java-content-handler=com.sun.mail.handlers.text_plain");
+        mc.addMailcap("multipart/*;; x-java-content-handler=com.sun.mail.handlers.multipart_mixed");
+        mc.addMailcap("message/rfc822;; x-java-content-handler=com.sun.mail.handlers.message_rfc822");
+        CommandMap.setDefaultCommandMap(mc);
+
         Properties props = new Properties();
         props.setProperty(MailParamsConstants.MAIL_SMTP_HOST, mailSmtpHost);
         props.setProperty(MailParamsConstants.MAIL_SMTP_PORT, mailSmtpPort);