diff --git a/backend/08-viewer.go b/backend/08-viewer.go
index c0336c0..3a361d2 100644
--- a/backend/08-viewer.go
+++ b/backend/08-viewer.go
@@ -18,7 +18,7 @@ import (
 // Lesebereich. Optional Weiterleiten einzelner Mails per SMTP (09-smtp.go).
 
 func viewerHandler(w http.ResponseWriter, r *http.Request) {
-	account := r.URL.Query().Get("account")
+	account := resolveViewerAccount(r.URL.Query().Get("account"), r.URL.Query().Get("source"))
 	folder := r.URL.Query().Get("folder")
 	q := strings.TrimSpace(r.URL.Query().Get("q"))
 	if account != "" && folder != "" {
@@ -33,7 +33,7 @@ func viewerHandler(w http.ResponseWriter, r *http.Request) {
 }
 
 func messageHandler(w http.ResponseWriter, r *http.Request) {
-	account := r.URL.Query().Get("account")
+	account := resolveViewerAccount(r.URL.Query().Get("account"), r.URL.Query().Get("source"))
 	folder := r.URL.Query().Get("folder")
 	targetAccount := r.URL.Query().Get("target_account")
 	index, err := strconv.Atoi(r.URL.Query().Get("index"))
@@ -65,7 +65,7 @@ func messageHandler(w http.ResponseWriter, r *http.Request) {
 }
 
 func targetMessageHandler(w http.ResponseWriter, r *http.Request) {
-	account := r.URL.Query().Get("account")
+	account := resolveViewerAccount(r.URL.Query().Get("account"), r.URL.Query().Get("source"))
 	folder := r.URL.Query().Get("folder")
 	targetAccount := r.URL.Query().Get("target_account")
 	index, err := strconv.Atoi(r.URL.Query().Get("index"))
@@ -112,11 +112,12 @@ func renderViewerTree(w http.ResponseWriter) {
 			continue
 		}
 		found = true
-		fmt.Fprintf(w, `<div class="tree-node account">%s</div>`, html.EscapeString(sourceAccountLabel(account)))
+		source := sourceAccountLabel(account)
+		fmt.Fprintf(w, `<div class="tree-node account">%s</div>`, html.EscapeString(source))
 		for _, path := range mboxes {
 			folder := strings.TrimSuffix(filepath.Base(path), ".mbox")
-			fmt.Fprintf(w, `<a class="tree-node" href="#" hx-get="/view?account=%s&amp;folder=%s" hx-target="#list" hx-swap="innerHTML">%s</a>`,
-				urlEsc(account), urlEsc(folder), html.EscapeString(folder))
+			fmt.Fprintf(w, `<a class="tree-node" href="#" hx-get="/view?source=%s&amp;folder=%s" hx-target="#list" hx-swap="innerHTML">%s</a>`,
+				urlEsc(source), urlEsc(folder), html.EscapeString(folder))
 		}
 	}
 	if !found {
@@ -142,11 +143,11 @@ func renderMessageList(w http.ResponseWriter, account, folder, q string) {
 	}
 	fmt.Fprintf(w, `<div class="pane-head">%s / %s (%d)</div>`, html.EscapeString(sourceAccountLabel(account)), html.EscapeString(folder), len(filtered))
 	fmt.Fprintf(w, `<form class="searchbar" hx-get="/view" hx-target="#list" hx-swap="innerHTML">
-<input type="hidden" name="account" value="%s">
+<input type="hidden" name="source" value="%s">
 <input type="hidden" name="folder" value="%s">
 <input class="input search-input" type="search" name="q" value="%s" placeholder="Suchen">
 <button class="btn secondary search-btn" type="submit">Suchen</button>
-</form>`, html.EscapeString(account), html.EscapeString(folder), html.EscapeString(q))
+</form>`, html.EscapeString(sourceAccountLabel(account)), html.EscapeString(folder), html.EscapeString(q))
 	for _, entry := range filtered {
 		subject := entry.Subject
 		if subject == "" {
@@ -156,8 +157,8 @@ func renderMessageList(w http.ResponseWriter, account, folder, q string) {
 		if from == "" {
 			from = "(ohne Absender)"
 		}
-		fmt.Fprintf(w, `<a class="msg-row" href="#" hx-get="/view/message?account=%s&amp;folder=%s&amp;index=%d" hx-include="#target-account-select" hx-target="#read" hx-swap="innerHTML"><span class="msg-from">%s</span><span class="msg-subject">%s</span><span class="msg-date">%s</span></a>`,
-			urlEsc(account), urlEsc(folder), entry.Index,
+		fmt.Fprintf(w, `<a class="msg-row" href="#" hx-get="/view/message?source=%s&amp;folder=%s&amp;index=%d" hx-include="#target-account-select" hx-target="#read" hx-swap="innerHTML"><span class="msg-from">%s</span><span class="msg-subject">%s</span><span class="msg-date">%s</span></a>`,
+			urlEsc(sourceAccountLabel(account)), urlEsc(folder), entry.Index,
 			html.EscapeString(from), html.EscapeString(subject), html.EscapeString(entry.Date))
 	}
 	if len(entries) == 0 {
@@ -336,11 +337,11 @@ func renderTargetAccountSelect(account, folder, selected string, index int) stri
 		fmt.Fprintf(&b, ` hx-get="/view/target" hx-target="#read-target" hx-swap="innerHTML" hx-trigger="change from:#target-account-select"`)
 	}
 	fmt.Fprintf(&b, `>
-<input type="hidden" name="account" value="%s">
+<input type="hidden" name="source" value="%s">
 <input type="hidden" name="folder" value="%s">
 <input type="hidden" name="index" value="%d">
 <select id="target-account-select" name="target_account" class="target-select">
-<option value="">Automatisch</option>`, html.EscapeString(account), html.EscapeString(folder), index)
+<option value="">Automatisch</option>`, html.EscapeString(sourceAccountLabel(account)), html.EscapeString(folder), index)
 	for _, opt := range options {
 		attr := ""
 		if opt.Value == selected {
@@ -393,6 +394,22 @@ func sourceAccountLabel(mboxDir string) string {
 	return mboxDir
 }
 
+func resolveViewerAccount(account, source string) string {
+	if strings.TrimSpace(account) != "" {
+		return account
+	}
+	source = strings.TrimSpace(source)
+	if source == "" {
+		return ""
+	}
+	for dir, label := range accountLabels() {
+		if strings.EqualFold(label.SourceLabel, source) {
+			return dir
+		}
+	}
+	return source
+}
+
 func accountLabels() map[string]viewerAccount {
 	out := map[string]viewerAccount{}
 	if DB == nil {