[MM-36872] add threading headers to notification emails (#18232)

* [MM-36872] Adding headers for mail threading

* MM-36872 Add message id and mail threading headers

* MM-36872 Add message id and mail threading headers

* MM-36872 Add msgId, inreplyto, references headers

* Fixing comment issues

* Applying gofmt lint fixes

* Applying gofmt lint fixes

* MM-36872: Updates required from merge.

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Martin Kraft <martin@upspin.org>

app/admin.go

@@ -231,7 +231,7 @@ func (a *App) TestEmail(userID string, cfg *model.Config) *model.AppError {
 	T := i18n.GetUserTranslations(user.Locale)
 	license := a.Srv().License()
 	mailConfig := a.Srv().MailServiceConfig()
-	if err := mail.SendMailUsingConfig(user.Email, T("api.admin.test_email.subject"), T("api.admin.test_email.body"), mailConfig, license != nil && *license.Features.Compliance, ""); err != nil {
+	if err := mail.SendMailUsingConfig(user.Email, T("api.admin.test_email.subject"), T("api.admin.test_email.body"), mailConfig, license != nil && *license.Features.Compliance, "", "", "", ""); err != nil {
 		return model.NewAppError("testEmail", "app.admin.test_email.failure", map[string]interface{}{"Error": err.Error()}, "", http.StatusInternalServerError)
 	}
 

app/admin_advisor.go

@@ -194,7 +194,7 @@ func (a *App) NotifyAndSetWarnMetricAck(warnMetricId string, sender *model.User,
 				return model.NewAppError("NotifyAndSetWarnMetricAck", "api.email.send_warn_metric_ack.failure.app_error", map[string]interface{}{"Error": err.Error()}, "", http.StatusInternalServerError)
 			}
 
-			if err := mail.SendMailUsingConfig(model.MmSupportAdvisorAddress, subject, body, mailConfig, false, sender.Email); err != nil {
+			if err := mail.SendMailUsingConfig(model.MmSupportAdvisorAddress, subject, body, mailConfig, false, "", "", "", sender.Email); err != nil {
 				return model.NewAppError("NotifyAndSetWarnMetricAck", "api.email.send_warn_metric_ack.failure.app_error", map[string]interface{}{"Error": err.Error()}, "", http.StatusInternalServerError)
 			}
 		}

app/email/email.go

@@ -625,7 +625,7 @@ func (es *Service) SendGuestInviteEmails(team *model.Team, channels []*model.Cha
 				mlog.Error("Failed to send invite email successfully", mlog.Err(err))
 			}
 
-			if nErr := es.SendMailWithEmbeddedFiles(invite, subject, body, embeddedFiles); nErr != nil {
+			if nErr := es.SendMailWithEmbeddedFiles(invite, subject, body, embeddedFiles, "", "", ""); nErr != nil {
 				mlog.Error("Failed to send invite email successfully", mlog.Err(nErr))
 				if errorWhenNotSent {
 					return SendMailError
@@ -769,7 +769,7 @@ func (es *Service) SendInviteEmailsToTeamAndChannels(
 			mlog.Error("Failed to send invite email successfully ", mlog.Err(err))
 		}
 
-		if nErr := es.SendMailWithEmbeddedFiles(invite, subject, body, embeddedFiles); nErr != nil {
+		if nErr := es.SendMailWithEmbeddedFiles(invite, subject, body, embeddedFiles, "", "", ""); nErr != nil {
 			mlog.Error("Failed to send invite email successfully", mlog.Err(nErr))
 			if errorWhenNotSent {
 				inviteWithError := &model.EmailInviteWithError{
@@ -832,7 +832,7 @@ func (es *Service) SendDeactivateAccountEmail(email string, locale, siteURL stri
 		return err
 	}
 
-	if err := es.sendMail(email, subject, body); err != nil {
+	if err := es.sendMail(email, subject, body); err != nil { // this needs to receive the header options
 		return err
 	}
 
@@ -854,21 +854,21 @@ func (es *Service) sendEmailWithCustomReplyTo(to, subject, htmlBody, replyToAddr
 	license := es.license()
 	mailConfig := es.mailServiceConfig(replyToAddress)
 
-	return mail.SendMailUsingConfig(to, subject, htmlBody, mailConfig, license != nil && *license.Features.Compliance, "")
+	return mail.SendMailUsingConfig(to, subject, htmlBody, mailConfig, license != nil && *license.Features.Compliance, "", "", "", "")
 }
 
 func (es *Service) sendMailWithCC(to, subject, htmlBody string, ccMail string) error {
 	license := es.license()
 	mailConfig := es.mailServiceConfig("")
 
-	return mail.SendMailUsingConfig(to, subject, htmlBody, mailConfig, license != nil && *license.Features.Compliance, ccMail)
+	return mail.SendMailUsingConfig(to, subject, htmlBody, mailConfig, license != nil && *license.Features.Compliance, "", "", "", ccMail)
 }
 
-func (es *Service) SendMailWithEmbeddedFiles(to, subject, htmlBody string, embeddedFiles map[string]io.Reader) error {
+func (es *Service) SendMailWithEmbeddedFiles(to, subject, htmlBody string, embeddedFiles map[string]io.Reader, messageID string, inReplyTo string, references string) error {
 	license := es.license()
 	mailConfig := es.mailServiceConfig("")
 
-	return mail.SendMailWithEmbeddedFilesUsingConfig(to, subject, htmlBody, embeddedFiles, mailConfig, license != nil && *license.Features.Compliance, "")
+	return mail.SendMailWithEmbeddedFilesUsingConfig(to, subject, htmlBody, embeddedFiles, mailConfig, license != nil && *license.Features.Compliance, messageID, inReplyTo, references, "")
 }
 
 func (es *Service) InvalidateVerifyEmailTokensForUser(userID string) *model.AppError {

app/email/email_batching.go

@@ -344,7 +344,7 @@ func (es *Service) sendBatchedEmailNotification(userID string, notifications []*
 		mlog.Error("Unable to render email", mlog.Err(renderErr))
 	}
 
-	if nErr := es.SendMailWithEmbeddedFiles(user.Email, subject, renderedPage, embeddedFiles); nErr != nil {
+	if nErr := es.SendMailWithEmbeddedFiles(user.Email, subject, renderedPage, embeddedFiles, "", "", ""); nErr != nil {
 		mlog.Warn("Unable to send batched email notification", mlog.String("email", user.Email), mlog.Err(nErr))
 	}
 }

app/email/mocks/ServiceInterface.go

@@ -302,13 +302,13 @@ func (_m *ServiceInterface) SendLicenseUpForRenewalEmail(_a0 string, name string
 	return r0
 }
 
-// SendMailWithEmbeddedFiles provides a mock function with given fields: to, subject, htmlBody, embeddedFiles
-func (_m *ServiceInterface) SendMailWithEmbeddedFiles(to string, subject string, htmlBody string, embeddedFiles map[string]io.Reader) error {
-	ret := _m.Called(to, subject, htmlBody, embeddedFiles)
+// SendMailWithEmbeddedFiles provides a mock function with given fields: to, subject, htmlBody, embeddedFiles, messageID, inReplyTo, references
+func (_m *ServiceInterface) SendMailWithEmbeddedFiles(to string, subject string, htmlBody string, embeddedFiles map[string]io.Reader, messageID string, inReplyTo string, references string) error {
+	ret := _m.Called(to, subject, htmlBody, embeddedFiles, messageID, inReplyTo, references)
 
 	var r0 error
-	if rf, ok := ret.Get(0).(func(string, string, string, map[string]io.Reader) error); ok {
-		r0 = rf(to, subject, htmlBody, embeddedFiles)
+	if rf, ok := ret.Get(0).(func(string, string, string, map[string]io.Reader, string, string, string) error); ok {
+		r0 = rf(to, subject, htmlBody, embeddedFiles, messageID, inReplyTo, references)
 	} else {
 		r0 = ret.Error(0)
 	}

app/email/service.go

@@ -142,7 +142,7 @@ type ServiceInterface interface {
 	SendInviteEmailsToTeamAndChannels(team *model.Team, channels []*model.Channel, senderName string, senderUserId string, senderProfileImage []byte, invites []string, siteURL string, reminderData *model.TeamInviteReminderData, message string, errorWhenNotSent bool) ([]*model.EmailInviteWithError, error)
 	SendDeactivateAccountEmail(email string, locale, siteURL string) error
 	SendNotificationMail(to, subject, htmlBody string) error
-	SendMailWithEmbeddedFiles(to, subject, htmlBody string, embeddedFiles map[string]io.Reader) error
+	SendMailWithEmbeddedFiles(to, subject, htmlBody string, embeddedFiles map[string]io.Reader, messageID string, inReplyTo string, references string) error
 	SendLicenseUpForRenewalEmail(email, name, locale, siteURL, renewalLink string, daysToExpiration int) error
 	SendPaymentFailedEmail(email string, locale string, failedPayment *model.FailedPayment, siteURL string) (bool, error)
 	SendNoCardPaymentFailedEmail(email string, locale string, siteURL string) error

app/notification_email.go

@@ -112,8 +112,23 @@ func (a *App) sendNotificationEmail(notification *PostNotification, user *model.
 		return errors.Wrap(err, "unable to render the email notification template")
 	}
 
+	templateString := "<%s@mattermost.com>"
+	messageID := ""
+	inReplyTo := ""
+	references := ""
+
+	if post.Id != "" {
+		messageID = fmt.Sprintf(templateString, post.Id)
+	}
+
+	if post.RootId != "" {
+		referencesVal := fmt.Sprintf(templateString, post.RootId)
+		inReplyTo = referencesVal
+		references = referencesVal
+	}
+
 	a.Srv().Go(func() {
-		if nErr := a.Srv().EmailService.SendMailWithEmbeddedFiles(user.Email, html.UnescapeString(subjectText), bodyText, embeddedFiles); nErr != nil {
+		if nErr := a.Srv().EmailService.SendMailWithEmbeddedFiles(user.Email, html.UnescapeString(subjectText), bodyText, embeddedFiles, messageID, inReplyTo, references); nErr != nil {
 			mlog.Error("Error while sending the email", mlog.String("user_email", user.Email), mlog.Err(nErr))
 		}
 	})

app/security_update_check.go

@@ -121,7 +121,7 @@ func (s *Server) DoSecurityUpdateCheck() {
 						mlog.Info("Sending security bulletin", mlog.String("bulletin_id", bulletin.Id), mlog.String("user_email", user.Email))
 						license := s.License()
 						mailConfig := s.MailServiceConfig()
-						mail.SendMailUsingConfig(user.Email, i18n.T("mattermost.bulletin.subject"), string(body), mailConfig, license != nil && *license.Features.Compliance, "")
+						mail.SendMailUsingConfig(user.Email, i18n.T("mattermost.bulletin.subject"), string(body), mailConfig, license != nil && *license.Features.Compliance, "", "", "", "")
 					}
 
 					bulletinSeen := &model.System{Name: "SecurityBulletin_" + bulletin.Id, Value: bulletin.Id}