webmail: fix for ignoring error about sending to invalid address

before, an error about an invalid address was not used, causing a delivery
attempt to an empty address (empty localpart/domain). delivery to that address
would fail, but we should've prevented that message from being queued at all.

additionally, an error in adding the message to the queue was ignored too.

queue/queue.go

@@ -253,6 +253,14 @@ func Add(ctx context.Context, log mlog.Log, senderAccount string, msgFile *os.Fi
 		if qm.ID != 0 {
 			return fmt.Errorf("id of queued messages must be 0")
 		}
+		if qm.RecipientDomainStr == "" {
+			return fmt.Errorf("recipient domain cannot be empty")
+		}
+		// Sanity check, internal consistency.
+		rcptDom := formatIPDomain(qm.RecipientDomain)
+		if qm.RecipientDomainStr != rcptDom {
+			return fmt.Errorf("mismatch between recipient domain and string form of domain")
+		}
 	}
 
 	if Localserve {

webmail/api.go

@@ -226,7 +226,7 @@ type File struct {
 func parseAddress(msghdr string) (message.NameAddress, error) {
 	a, err := mail.ParseAddress(msghdr)
 	if err != nil {
-		return message.NameAddress{}, nil
+		return message.NameAddress{}, err
 	}
 
 	// todo: parse more fully according to ../rfc/5322:959
@@ -341,12 +341,12 @@ func (w Webmail) MessageSubmit(ctx context.Context, m SubmitMessage) {
 	}
 	if err != nil && (errors.Is(err, mox.ErrAccountNotFound) || errors.Is(err, mox.ErrDomainNotFound)) {
 		metricSubmission.WithLabelValues("badfrom").Inc()
-		xcheckuserf(ctx, errors.New("address not found"), "looking from address for account")
+		xcheckuserf(ctx, errors.New("address not found"), `looking up "from" address for account`)
 	}
 	xcheckf(ctx, err, "checking if from address is allowed")
 
 	if len(recipients) == 0 {
-		xcheckuserf(ctx, fmt.Errorf("no recipients"), "composing message")
+		xcheckuserf(ctx, errors.New("no recipients"), "composing message")
 	}
 
 	// Check outgoing message rate limit.
@@ -657,7 +657,8 @@ func (w Webmail) MessageSubmit(ctx context.Context, m SubmitMessage) {
 		}
 		qml[i] = qm
 	}
-	if err := queue.Add(ctx, log, reqInfo.AccountName, dataFile, qml...); err != nil {
+	err = queue.Add(ctx, log, reqInfo.AccountName, dataFile, qml...)
+	if err != nil {
 		metricSubmission.WithLabelValues("queueerror").Inc()
 	}
 	xcheckf(ctx, err, "adding messages to the delivery queue")