use batch send mail

etc/server.conf

@@ -61,6 +61,7 @@ User = "username"
 Pass = "password"
 From = "username@163.com"
 InsecureSkipVerify = true
+Batch = 5
 
 [Alerting]
 TemplatesDir = "./etc/template"

src/server/config/config.go

@@ -131,6 +131,7 @@ type SMTPConfig struct {
 	Pass               string
 	From               string
 	InsecureSkipVerify bool
+	Batch              int
 }
 
 type Alerting struct {

src/server/engine/engine.go

@@ -5,6 +5,7 @@ import (
 	"time"
 
 	"github.com/didi/nightingale/v5/src/server/config"
+	"github.com/didi/nightingale/v5/src/server/sender"
 	promstat "github.com/didi/nightingale/v5/src/server/stat"
 )
 
@@ -22,6 +23,8 @@ func Start(ctx context.Context) error {
 
 	go reportQueueSize()
 
+	go sender.StartEmailSender()
+
 	return nil
 }
 

src/server/engine/notify.go

@@ -175,7 +175,7 @@ func handleNotice(notice Notice, bs []byte) {
 				content = "mailbody.tpl not found"
 			}
 
-			sender.SendEmail(subject, content, StringSetKeys(emailset))
+			sender.WriteEmail(subject, content, StringSetKeys(emailset))
 		case "dingtalk":
 			if len(dingtalkset) == 0 {
 				continue

src/server/sender/email.go

@@ -67,19 +67,45 @@ func StartEmailSender() {
 
 	var s gomail.SendCloser
 	var open bool
+	var size int
 	for {
 		select {
 		case m, ok := <-mailch:
 			if !ok {
 				return
 			}
+
 			if !open {
 				s = dialSmtp(d)
 				open = true
 			}
+
 			if err := gomail.Send(s, m); err != nil {
 				logger.Errorf("email_sender: failed to send: %s", err)
+
+				// close and retry
+				if err := s.Close(); err != nil {
+					logger.Warningf("email_sender: failed to close smtp connection: %s", err)
 				}
+
+				s = dialSmtp(d)
+				open = true
+
+				if err := gomail.Send(s, m); err != nil {
+					logger.Errorf("email_sender: failed to retry send: %s", err)
+				}
+			}
+
+			size++
+
+			if size >= conf.Batch {
+				if err := s.Close(); err != nil {
+					logger.Warningf("email_sender: failed to close smtp connection: %s", err)
+				}
+				open = false
+				size = 0
+			}
+
 		// Close the connection to the SMTP server if no email was sent in
 		// the last 30 seconds.
 		case <-time.After(30 * time.Second):