diff --git a/components/identity/identity-form.tsx b/components/identity/identity-form.tsx
index 71cd5313..1dbefb65 100644
--- a/components/identity/identity-form.tsx
+++ b/components/identity/identity-form.tsx
@@ -8,6 +8,31 @@ import type { Identity, EmailAddress } from '@/lib/jmap/types';
 import { sanitizeSignatureHtml } from '@/lib/email-sanitization';
 import { getEmailValidationError, validateEmailList } from '@/lib/validation';
 
+// JMAP Identity/set caps signature fields at 2047 UTF-8 bytes per RFC 8621 §6.1.
+const SIGNATURE_MAX_BYTES = 2047;
+const utf8Encoder = new TextEncoder();
+
+function utf8ByteLength(s: string): number {
+  return utf8Encoder.encode(s).length;
+}
+
+function truncateToUtf8Bytes(s: string, maxBytes: number): string {
+  if (utf8ByteLength(s) <= maxBytes) return s;
+  let lo = 0;
+  let hi = s.length;
+  while (lo < hi) {
+    const mid = (lo + hi + 1) >>> 1;
+    if (utf8ByteLength(s.slice(0, mid)) <= maxBytes) lo = mid;
+    else hi = mid - 1;
+  }
+  // Don't split a surrogate pair: if we landed right after a high surrogate, back off one code unit.
+  if (lo > 0) {
+    const prev = s.charCodeAt(lo - 1);
+    if (prev >= 0xD800 && prev <= 0xDBFF) lo -= 1;
+  }
+  return s.slice(0, lo);
+}
+
 interface IdentityFormData {
   name: string;
   email: string;
@@ -246,14 +271,15 @@ export function IdentityForm({ identity, onSave, onCancel }: IdentityFormProps)
         </label>
         <textarea
           id="identity-text-sig"
-          maxLength={2000}
           value={formData.textSignature}
-          onChange={(e) => setFormData({ ...formData, textSignature: e.target.value })}
+          onChange={(e) => setFormData({ ...formData, textSignature: truncateToUtf8Bytes(e.target.value, SIGNATURE_MAX_BYTES) })}
           rows={3}
           disabled={isSubmitting}
           aria-label={t('text_signature_label')}
+          aria-describedby="identity-text-sig-counter"
           className="flex w-full rounded-md border border-input bg-background px-3 py-2 text-sm text-foreground transition-all duration-200 placeholder:text-muted-foreground hover:border-muted-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:border-ring disabled:cursor-not-allowed disabled:opacity-50"
         />
+        <SignatureByteCounter id="identity-text-sig-counter" value={formData.textSignature || ''} />
       </div>
 
       {/* HTML Signature */}
@@ -263,14 +289,15 @@ export function IdentityForm({ identity, onSave, onCancel }: IdentityFormProps)
         </label>
         <textarea
           id="identity-html-sig"
-          maxLength={50000}
           value={formData.htmlSignature}
-          onChange={(e) => setFormData({ ...formData, htmlSignature: e.target.value })}
+          onChange={(e) => setFormData({ ...formData, htmlSignature: truncateToUtf8Bytes(e.target.value, SIGNATURE_MAX_BYTES) })}
           rows={5}
           disabled={isSubmitting}
           aria-label={t('html_signature_label')}
+          aria-describedby="identity-html-sig-counter"
           className="flex w-full rounded-md border border-input bg-background px-3 py-2 text-sm text-foreground font-mono transition-all duration-200 placeholder:text-muted-foreground hover:border-muted-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:border-ring disabled:cursor-not-allowed disabled:opacity-50"
         />
+        <SignatureByteCounter id="identity-html-sig-counter" value={formData.htmlSignature || ''} />
         {formData.htmlSignature && (
           <div className="mt-2 p-2 border rounded bg-muted">
             <div className="text-xs text-muted-foreground mb-1">{tDisplay('preview')}</div>
@@ -304,3 +331,26 @@ export function IdentityForm({ identity, onSave, onCancel }: IdentityFormProps)
     </form>
   );
 }
+
+function SignatureByteCounter({ id, value }: { id: string; value: string }) {
+  const t = useTranslations('identities.form');
+  const bytes = utf8ByteLength(value);
+  const atLimit = bytes >= SIGNATURE_MAX_BYTES;
+  const nearLimit = !atLimit && bytes >= Math.floor(SIGNATURE_MAX_BYTES * 0.9);
+  const tone = atLimit
+    ? 'text-destructive'
+    : nearLimit
+      ? 'text-amber-600 dark:text-amber-400'
+      : 'text-muted-foreground';
+  return (
+    <p
+      id={id}
+      className={`text-xs mt-1 tabular-nums ${tone}`}
+      role="status"
+      aria-live="polite"
+    >
+      {t('signature_byte_counter', { bytes, max: SIGNATURE_MAX_BYTES })}
+      {atLimit && <span className="ml-1">{t('signature_byte_limit_reached')}</span>}
+    </p>
+  );
+}
diff --git a/locales/cs/common.json b/locales/cs/common.json
index f95ad516..98d3b5fc 100644
--- a/locales/cs/common.json
+++ b/locales/cs/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "archiv@email.com",
       "text_signature_label": "Textový podpis",
       "html_signature_label": "HTML podpis",
+      "signature_byte_counter": "{bytes} / {max} bajtů",
+      "signature_byte_limit_reached": "Dosažen limit serveru",
       "save": "Uložit identitu",
       "cancel": "Zrušit",
       "creating": "Vytváření...",
diff --git a/locales/da/common.json b/locales/da/common.json
index 257859fb..a5645a08 100644
--- a/locales/da/common.json
+++ b/locales/da/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "arkiv@email.dk",
       "text_signature_label": "Tekstsignatur",
       "html_signature_label": "HTML-signatur",
+      "signature_byte_counter": "{bytes} / {max} bytes",
+      "signature_byte_limit_reached": "Servergrænse nået",
       "save": "Gem identitet",
       "cancel": "Annuller",
       "creating": "Opretter...",
diff --git a/locales/de/common.json b/locales/de/common.json
index 71c5f5d3..2905164b 100644
--- a/locales/de/common.json
+++ b/locales/de/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "archiv@email.de",
       "text_signature_label": "Text-Signatur",
       "html_signature_label": "HTML-Signatur",
+      "signature_byte_counter": "{bytes} / {max} Bytes",
+      "signature_byte_limit_reached": "Serverlimit erreicht",
       "save": "Identität speichern",
       "cancel": "Abbrechen",
       "creating": "Wird erstellt...",
diff --git a/locales/en/common.json b/locales/en/common.json
index 1f5b7722..f4c53d62 100644
--- a/locales/en/common.json
+++ b/locales/en/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "archive@email.com",
       "text_signature_label": "Text Signature",
       "html_signature_label": "HTML Signature",
+      "signature_byte_counter": "{bytes} / {max} bytes",
+      "signature_byte_limit_reached": "Server limit reached",
       "save": "Save Identity",
       "cancel": "Cancel",
       "creating": "Creating...",
diff --git a/locales/es/common.json b/locales/es/common.json
index de400948..59055750 100644
--- a/locales/es/common.json
+++ b/locales/es/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "archivo@correo.com",
       "text_signature_label": "Firma de Texto",
       "html_signature_label": "Firma HTML",
+      "signature_byte_counter": "{bytes} / {max} bytes",
+      "signature_byte_limit_reached": "Límite del servidor alcanzado",
       "save": "Guardar Identidad",
       "cancel": "Cancelar",
       "creating": "Creando...",
diff --git a/locales/fr/common.json b/locales/fr/common.json
index 97fa228a..926687bd 100644
--- a/locales/fr/common.json
+++ b/locales/fr/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "archive@email.com",
       "text_signature_label": "Signature texte",
       "html_signature_label": "Signature HTML",
+      "signature_byte_counter": "{bytes} / {max} octets",
+      "signature_byte_limit_reached": "Limite du serveur atteinte",
       "save": "Enregistrer l'identité",
       "cancel": "Annuler",
       "creating": "Création...",
diff --git a/locales/it/common.json b/locales/it/common.json
index ce0a8a05..0c7db1d3 100644
--- a/locales/it/common.json
+++ b/locales/it/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "archivio@email.com",
       "text_signature_label": "Firma di testo",
       "html_signature_label": "Firma HTML",
+      "signature_byte_counter": "{bytes} / {max} byte",
+      "signature_byte_limit_reached": "Limite del server raggiunto",
       "save": "Salva identità",
       "cancel": "Annulla",
       "creating": "Creazione...",
diff --git a/locales/ja/common.json b/locales/ja/common.json
index 164467dd..c33062bc 100644
--- a/locales/ja/common.json
+++ b/locales/ja/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "archive@email.com",
       "text_signature_label": "テキスト署名",
       "html_signature_label": "HTML署名",
+      "signature_byte_counter": "{bytes} / {max} バイト",
+      "signature_byte_limit_reached": "サーバーの上限に達しました",
       "save": "送信者情報を保存",
       "cancel": "キャンセル",
       "creating": "作成中...",
diff --git a/locales/ko/common.json b/locales/ko/common.json
index dbf3c732..e0fa72f8 100644
--- a/locales/ko/common.json
+++ b/locales/ko/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "archive@email.com",
       "text_signature_label": "텍스트 서명",
       "html_signature_label": "HTML 서명",
+      "signature_byte_counter": "{bytes} / {max} 바이트",
+      "signature_byte_limit_reached": "서버 한도 도달",
       "save": "저장",
       "cancel": "취소",
       "creating": "만드는 중...",
diff --git a/locales/lv/common.json b/locales/lv/common.json
index 5ed953d4..8e429169 100644
--- a/locales/lv/common.json
+++ b/locales/lv/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "arhivs@piemers.lv",
       "text_signature_label": "Teksta paraksts",
       "html_signature_label": "HTML paraksts",
+      "signature_byte_counter": "{bytes} / {max} baiti",
+      "signature_byte_limit_reached": "Sasniegts servera ierobežojums",
       "save": "Saglabāt identitāti",
       "cancel": "Atcelt",
       "creating": "Izveido...",
diff --git a/locales/nl/common.json b/locales/nl/common.json
index 597c4255..f528f2f1 100644
--- a/locales/nl/common.json
+++ b/locales/nl/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "archief@email.nl",
       "text_signature_label": "Teksthandtekening",
       "html_signature_label": "HTML-handtekening",
+      "signature_byte_counter": "{bytes} / {max} bytes",
+      "signature_byte_limit_reached": "Serverlimiet bereikt",
       "save": "Identiteit opslaan",
       "cancel": "Annuleren",
       "creating": "Aanmaken...",
diff --git a/locales/pl/common.json b/locales/pl/common.json
index 42231500..4af772dd 100644
--- a/locales/pl/common.json
+++ b/locales/pl/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "archive@email.com",
       "text_signature_label": "Podpis tekstowy",
       "html_signature_label": "Podpis HTML",
+      "signature_byte_counter": "{bytes} / {max} bajtów",
+      "signature_byte_limit_reached": "Osiągnięto limit serwera",
       "save": "Zapisz tożsamość",
       "cancel": "Anuluj",
       "creating": "Tworzenie...",
diff --git a/locales/pt/common.json b/locales/pt/common.json
index 2b8dcf51..7b1790f4 100644
--- a/locales/pt/common.json
+++ b/locales/pt/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "arquivo@email.com",
       "text_signature_label": "Assinatura de Texto",
       "html_signature_label": "Assinatura HTML",
+      "signature_byte_counter": "{bytes} / {max} bytes",
+      "signature_byte_limit_reached": "Limite do servidor atingido",
       "save": "Salvar Identidade",
       "cancel": "Cancelar",
       "creating": "Criando...",
diff --git a/locales/ru/common.json b/locales/ru/common.json
index 29f03131..975e9672 100644
--- a/locales/ru/common.json
+++ b/locales/ru/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "archive@пример.рф",
       "text_signature_label": "Текстовая подпись",
       "html_signature_label": "HTML-подпись",
+      "signature_byte_counter": "{bytes} / {max} байт",
+      "signature_byte_limit_reached": "Достигнут лимит сервера",
       "save": "Сохранить идентификацию",
       "cancel": "Отмена",
       "creating": "Создание...",
diff --git a/locales/tr/common.json b/locales/tr/common.json
index fc90a304..b607e9be 100644
--- a/locales/tr/common.json
+++ b/locales/tr/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "arsiv@email.com",
       "text_signature_label": "Metin İmzası",
       "html_signature_label": "HTML İmzası",
+      "signature_byte_counter": "{bytes} / {max} bayt",
+      "signature_byte_limit_reached": "Sunucu sınırına ulaşıldı",
       "save": "Kimliği Kaydet",
       "cancel": "İptal",
       "creating": "Oluşturuluyor...",
diff --git a/locales/uk/common.json b/locales/uk/common.json
index 8f408cdf..13d37a57 100644
--- a/locales/uk/common.json
+++ b/locales/uk/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "archive@email.com",
       "text_signature_label": "Текстовий підпис",
       "html_signature_label": "Підпис HTML",
+      "signature_byte_counter": "{bytes} / {max} байтів",
+      "signature_byte_limit_reached": "Досягнуто обмеження сервера",
       "save": "Зберегти ідентифікатор",
       "cancel": "Скасувати",
       "creating": "Створення...",
diff --git a/locales/zh/common.json b/locales/zh/common.json
index e4644b96..1adb52e5 100644
--- a/locales/zh/common.json
+++ b/locales/zh/common.json
@@ -1863,6 +1863,8 @@
       "bcc_placeholder": "archive@example.com",
       "text_signature_label": "文字签名",
       "html_signature_label": "HTML 签名",
+      "signature_byte_counter": "{bytes} / {max} 字节",
+      "signature_byte_limit_reached": "已达服务器限制",
       "save": "保存身份",
       "cancel": "取消",
       "creating": "创建中...",