[bugfix] add Date and Message-ID headers for email (#3031)

* [bugfix] add Date and Message-ID headers for email

This should make spam filters more happy, as most of them grant some
negative score for not having those headers. Also the Date is convenient
for the user receiving the mail.

* make golangci-lint happy

1 files changed, 6 insertions, 2 deletions

diff --git a/internal/email/common.go b/internal/email/common.go
index 5864a82f7..25a469a39 100644
--- a/internal/email/common.go
+++ b/internal/email/common.go
@@ -26,7 +26,9 @@ import (
 	"path/filepath"
 	"strings"
 	"text/template"
+	"time"
 
+	"github.com/google/uuid"
 	"github.com/superseriousbusiness/gotosocial/internal/config"
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 )
@@ -37,7 +39,7 @@ func (s *sender) sendTemplate(template string, subject string, data any, toAddre
 		return err
 	}
 
-	msg, err := assembleMessage(subject, buf.String(), s.from, toAddresses...)
+	msg, err := assembleMessage(subject, buf.String(), s.from, s.msgIDHost, toAddresses...)
 	if err != nil {
 		return err
 	}
@@ -65,7 +67,7 @@ func loadTemplates(templateBaseDir string) (*template.Template, error) {
 // assembleMessage assembles a valid email message following:
 //   - https://datatracker.ietf.org/doc/html/rfc2822
 //   - https://pkg.go.dev/net/smtp#SendMail
-func assembleMessage(mailSubject string, mailBody string, mailFrom string, mailTo ...string) ([]byte, error) {
+func assembleMessage(mailSubject string, mailBody string, mailFrom string, msgIDHost string, mailTo ...string) ([]byte, error) {
 	if strings.ContainsAny(mailSubject, "\r\n") {
 		return nil, errors.New("email subject must not contain newline characters")
 	}
@@ -103,7 +105,9 @@ func assembleMessage(mailSubject string, mailBody string, mailFrom string, mailT
 		// msg headers.'
 		msg.WriteString("To: Undisclosed Recipients:;" + CRLF)
 	}
+	msg.WriteString("Date: " + time.Now().Format(time.RFC822Z) + CRLF)
 	msg.WriteString("From: " + mailFrom + CRLF)
+	msg.WriteString("Message-ID: <" + uuid.New().String() + "@" + msgIDHost + ">" + CRLF)
 	msg.WriteString("Subject: " + mailSubject + CRLF)
 	msg.WriteString("MIME-Version: 1.0" + CRLF)
 	msg.WriteString("Content-Transfer-Encoding: 8bit" + CRLF)