diff --git a/app/notification_email.go b/app/notification_email.go
index 2736ac7213..9690152a57 100644
--- a/app/notification_email.go
+++ b/app/notification_email.go
@@ -113,7 +113,7 @@ func (a *App) sendNotificationEmail(c request.CTX, notification *PostNotificatio
 		return errors.Wrap(err, "unable to render the email notification template")
 	}
 
-	templateString := "<%s@mattermost.com>"
+	templateString := "<%s@" + utils.GetHostnameFromSiteURL(a.GetSiteURL()) + ">"
 	messageID := ""
 	inReplyTo := ""
 	references := ""
diff --git a/shared/mail/mail.go b/shared/mail/mail.go
index 03dbddc62a..e0ced44a5a 100644
--- a/shared/mail/mail.go
+++ b/shared/mail/mail.go
@@ -6,6 +6,7 @@ package mail
 import (
 	"context"
 	"crypto/tls"
+	"fmt"
 	"io"
 	"mime"
 	"net"
@@ -17,6 +18,7 @@ import (
 	"github.com/pkg/errors"
 	gomail "gopkg.in/mail.v2"
 
+	"github.com/mattermost/mattermost-server/v6/model"
 	"github.com/mattermost/mattermost-server/v6/shared/mlog"
 )
 
@@ -282,10 +284,10 @@ func sendMailUsingConfigAdvanced(mail mailData, config *SMTPConfig) error {
 	defer c.Quit()
 	defer c.Close()
 
-	return SendMail(c, mail, time.Now())
+	return sendMail(c, mail, time.Now(), config)
 }
 
-func SendMail(c smtpClient, mail mailData, date time.Time) error {
+func sendMail(c smtpClient, mail mailData, date time.Time, config *SMTPConfig) error {
 	mlog.Debug("sending mail", mlog.String("to", mail.smtpTo), mlog.String("subject", mail.subject))
 
 	htmlMessage := mail.htmlBody
@@ -315,6 +317,10 @@ func SendMail(c smtpClient, mail mailData, date time.Time) error {
 
 	if mail.messageID != "" {
 		headers["Message-ID"] = []string{mail.messageID}
+	} else {
+		randomStringLength := 16
+		msgID := fmt.Sprintf("<%s-%d@%s>", model.NewRandomString(randomStringLength), time.Now().Unix(), config.Hostname)
+		headers["Message-ID"] = []string{msgID}
 	}
 
 	if mail.inReplyTo != "" {
diff --git a/shared/mail/mail_test.go b/shared/mail/mail_test.go
index ff5c0cd71c..202294d134 100644
--- a/shared/mail/mail_test.go
+++ b/shared/mail/mail_test.go
@@ -363,13 +363,13 @@ func TestSendMail(t *testing.T) {
 			"\r\nMessage-ID: <abc123@mattermost.com>\r\n",
 			"",
 		},
-		"doesn't add message-id header": {
+		"always adds message-id header": {
 			mail.Address{},
 			"",
 			"",
 			"",
+			"\r\nMessage-ID: <",
 			"",
-			"\r\nMessage-ID:",
 		},
 		"adds in-reply-to header": {
 			mail.Address{},
@@ -408,7 +408,8 @@ func TestSendMail(t *testing.T) {
 	for testName, tc := range testCases {
 		t.Run(testName, func(t *testing.T) {
 			mail := mailData{"", "", mail.Address{}, "", tc.replyTo, "", "", nil, nil, tc.messageID, tc.inReplyTo, tc.references}
-			err = SendMail(mocm, mail, time.Now())
+			cfg := getConfig()
+			err = sendMail(mocm, mail, time.Now(), cfg)
 			require.NoError(t, err)
 			if tc.contains != "" {
 				require.Contains(t, string(mocm.data), tc.contains)