diff --git a/rfc/index.txt b/rfc/index.txt
index d65947d..08372c7 100644
--- a/rfc/index.txt
+++ b/rfc/index.txt
@@ -32,6 +32,7 @@ Also see IANA assignments, https://www.iana.org/protocols
 2231	Yes	-	MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations
 3629	-	-	UTF-8, a transformation format of ISO 10646
 3676	No	-	The Text/Plain Format and DelSp Parameters
+4155	-	-	The application/mbox Media Type
 5234	-	-	Augmented BNF for Syntax Specifications: ABNF
 5322	Yes	-	Internet Message Format
 5598	-	-	Internet Mail Architecture
diff --git a/store/export.go b/store/export.go
index 7a8075b..3152e88 100644
--- a/store/export.go
+++ b/store/export.go
@@ -400,6 +400,7 @@ func exportMailbox(log mlog.Log, tx *bstore.Tx, accountDir string, mailboxID int
 		if m.MailFrom != "" {
 			mailfrom = m.MailFrom
 		}
+		// ../rfc/4155:80
 		if _, err := fmt.Fprintf(mboxwriter, "From %s %s\n", mailfrom, m.Received.Format(time.ANSIC)); err != nil {
 			return fmt.Errorf("write message line to mbox temp file: %v", err)
 		}
@@ -450,6 +451,8 @@ func exportMailbox(log mlog.Log, tx *bstore.Tx, accountDir string, mailboxID int
 			}
 		}
 
+		// ../rfc/4155:365 todo: rewrite messages to be 7-bit. still useful nowadays?
+
 		header := true
 		r := bufio.NewReader(mr)
 		for {
@@ -458,6 +461,7 @@ func exportMailbox(log mlog.Log, tx *bstore.Tx, accountDir string, mailboxID int
 				return fmt.Errorf("reading message: %v", rerr)
 			}
 			if len(line) > 0 {
+				// ../rfc/4155:354
 				if bytes.HasSuffix(line, []byte("\r\n")) {
 					line = line[:len(line)-1]
 					line[len(line)-1] = '\n'
@@ -473,6 +477,7 @@ func exportMailbox(log mlog.Log, tx *bstore.Tx, accountDir string, mailboxID int
 						continue
 					}
 				}
+				// ../rfc/4155:119
 				if bytes.HasPrefix(bytes.TrimLeft(line, ">"), []byte("From ")) {
 					if _, err := fmt.Fprint(mboxwriter, ">"); err != nil {
 						return fmt.Errorf("writing escaping >: %v", err)
@@ -486,6 +491,7 @@ func exportMailbox(log mlog.Log, tx *bstore.Tx, accountDir string, mailboxID int
 				break
 			}
 		}
+		// ../rfc/4155:75
 		if _, err := fmt.Fprint(mboxwriter, "\n"); err != nil {
 			return fmt.Errorf("writing end of message newline: %v", err)
 		}
diff --git a/store/import.go b/store/import.go
index dbce333..0f2e496 100644
--- a/store/import.go
+++ b/store/import.go
@@ -100,7 +100,7 @@ func (mr *MboxReader) Next() (*Message, *os.File, string, error) {
 		}
 		if len(line) > 0 {
 			mr.line++
-			// We store data with crlf, adjust any imported messages with bare newlines.
+			// We store data with crlf, adjust any imported messages with bare newlines. ../rfc/4155:354
 			if !bytes.HasSuffix(line, []byte("\r\n")) {
 				line = append(line[:len(line)-1], "\r\n"...)
 			}
@@ -156,12 +156,13 @@ func (mr *MboxReader) Next() (*Message, *os.File, string, error) {
 				mr.header = false
 			}
 
-			// Next mail message starts at bare From word.
+			// Next mail message starts at bare From word. ../rfc/4155:71
 			if mr.prevempty && bytes.HasPrefix(line, from) {
 				mr.fromLine = strings.TrimSpace(string(line))
 				mr.header = true
 				break
 			}
+			// ../rfc/4155:119
 			if bytes.HasPrefix(line, []byte(">")) && bytes.HasPrefix(bytes.TrimLeft(line, ">"), []byte("From ")) {
 				line = line[1:]
 			}