(setq default-mime-charset 'koi8-r) In `mime/editor-mode': calling `mime-editor/set-transfer-level-8bit'; writing message: Headers: --[[text/plain]] 8-bit text --[[text/plain]] 8-bit text calling `mime-editor/exit'. It generates the following buffer contents (shifted to right to avoid interpreting as multipart mime entity). Headers: Mime-Version: 1.0 (generated by tm-edit 1.8) Content-Type: multipart/mixed; boundary="Multipart_Mon_Sep_29_19:15:26_2003-1" Content-Transfer-Encoding: 7bit --Multipart_Mon_Sep_29_19:15:26_2003-1 Content-Type: text/plain; charset=KOI8-R Content-Transfer-Encoding: 8bit 8-bit text --Multipart_Mon_Sep_29_19:15:26_2003-1 Content-Type: text/plain; charset=KOI8-R Content-Transfer-Encoding: 8bit 8-bit text --Multipart_Mon_Sep_29_19:15:26_2003-1-- Content-Transfer-Encoding is set to 8bit for message body parts, so the entire message is 8bit. But Content-Transfer-Encoding is set to 7bit in header of message (as multipart/mixed entity). This causes some mail UA's to cut higher bit in 8bit body parts on receiving.