add "RcptTo" to webapi MessageGet result

otherwise, if the recipient was a bcc, there's no good way to see why the
message was received.

incoming webhooks already have this rcptto field, but that's not always the
moment you want to process it.

for mattanja on matrix, thanks for reporting!

webapi/doc.go

@@ -238,9 +238,10 @@ Get a message in parsed form:
 				"$notjunk",
 				"\seen"
 			],
-			"MailFrom": "",
+			"MailFrom": "mox@localhost",
+			"RcptTo": "mox@localhost",
 			"MailFromValidated": false,
-			"MsgFrom": "",
+			"MsgFrom": "mox@localhost",
 			"MsgFromValidated": false,
 			"DKIMVerifiedDomains": [],
 			"RemoteIP": "",

webapi/gendoc.sh

@@ -249,9 +249,10 @@ Get a message in parsed form:
 				"\$notjunk",
 				"\\seen"
 			],
-			"MailFrom": "",
+			"MailFrom": "mox@localhost",
+			"RcptTo": "mox@localhost",
 			"MailFromValidated": false,
-			"MsgFrom": "",
+			"MsgFrom": "mox@localhost",
 			"MsgFromValidated": false,
 			"DKIMVerifiedDomains": [],
 			"RemoteIP": "",

webapi/webapi.go

@@ -157,8 +157,9 @@ type MessageMeta struct {
 	Size                int64    // Total size of raw message file.
 	DSN                 bool     // Whether this message is a DSN.
 	Flags               []string // Standard message flags like \seen, \answered, $forwarded, $junk, $nonjunk, and custom keywords.
-	MailFrom            string   // Address used during SMTP "MAIL FROM" command.
+	MailFrom            string   // Address used during SMTP "MAIL FROM" command. Unicode.
 	MailFromValidated   bool     // Whether SMTP MAIL FROM address was SPF-validated.
+	RcptTo              string   // Address delivered to with SMTP "RCPT TO" command. Unicode.
 	MsgFrom             string   // Address used in message "From" header.
 	MsgFromValidated    bool     // Whether address in message "From"-header was DMARC(-like) validated.
 	DKIMVerifiedDomains []string // Verified domains from DKIM-signature in message. Can be different domain than used in addresses.

webapisrv/server.go

@@ -1245,12 +1245,17 @@ func (s server) MessageGet(ctx context.Context, req webapi.MessageGetRequest) (r
 	if d, err := dns.ParseDomain(m.MsgFromDomain); err == nil {
 		msgFrom = smtp.NewAddress(m.MsgFromLocalpart, d).Pack(true)
 	}
+	var rcptTo string
+	if m.RcptToDomain != "" {
+		rcptTo = m.RcptToLocalpart.String() + "@" + m.RcptToDomain
+	}
 	meta := webapi.MessageMeta{
 		Size:                m.Size,
 		DSN:                 m.DSN,
 		Flags:               append(m.Flags.Strings(), m.Keywords...),
 		MailFrom:            m.MailFrom,
 		MailFromValidated:   m.MailFromValidated,
+		RcptTo:              rcptTo,
 		MsgFrom:             msgFrom,
 		MsgFromValidated:    m.MsgFromValidated,
 		DKIMVerifiedDomains: m.DKIMDomains,