fix: replace, don't add, transfer encoding when making body 7-bit clean

Changelog.md

@@ -4,19 +4,28 @@ Changelog [format](http://keepachangelog.com/en/1.0.0/)
 
 ## Unreleased
 
+## [Bridge 1.4.4] Forth
+
+### Fixed
+* GODT-798 Replace, don't add, transfer encoding when making body 7-bit clean.
+
+
 ## [Bridge 1.4.3] Forth
 
 ### Changed
 * Reverted sending IMAP updates to be not blocking again.
+
 ### Fixed
 * GODT-783 Settings flags by FLAGS (not using +/-FLAGS) do not change spam state.
 
+
 ## [Bridge 1.4.2] Forth
 
 ### Changed
 * GODT-761 Use label.Path instead of Name to partially support subfolders for webapp beta release.
 * GODT-765 Improve speed of checking whether message is deleted.
 
+
 ## [IE 1.1.1] Danube (beta 2020-09-xx) [Bridge 1.4.1] Forth (beta 2020-09-xx)
 
 ### Fixed
@@ -24,12 +33,14 @@ Changelog [format](http://keepachangelog.com/en/1.0.0/)
 * GODT-752 Parsing non-utf8 multipart/alternative message.
 * GODT-752 Parsing message with duplicate charset parameter.
 
+
 ## [IE 1.1.0] Danube
 
 ### Fixed
 * GODT-703 Import-Export showed always at least one total message.
 * GODT-738 Fix for mbox files with long lines.
 
+
 ## [Bridge 1.4.0] Forth
 
 ### Added

pkg/message/parser/writer.go

@@ -35,7 +35,7 @@ func newWriter(root *Part) *Writer {
 
 func (w *Writer) Write(ww io.Writer) error {
 	if !w.root.is7BitClean() {
-		w.root.Header.Add("Content-Transfer-Encoding", "base64")
+		w.root.Header.Set("Content-Transfer-Encoding", "base64")
 	}
 
 	msgWriter, err := message.CreateWriter(ww, w.root.Header)
@@ -68,7 +68,7 @@ func (w *Writer) write(writer *message.Writer, p *Part) error {
 
 func (w *Writer) writeAsChild(writer *message.Writer, p *Part) error {
 	if !p.is7BitClean() {
-		p.Header.Add("Content-Transfer-Encoding", "base64")
+		p.Header.Set("Content-Transfer-Encoding", "base64")
 	}
 
 	childWriter, err := writer.CreatePart(p.Header)