[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/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