diff --git a/app/[locale]/page.tsx b/app/[locale]/page.tsx
index fda1d125..0c5a51a4 100644
--- a/app/[locale]/page.tsx
+++ b/app/[locale]/page.tsx
@@ -1551,6 +1551,7 @@ export default function Home() {
                   mode={pendingDraft?.mode ?? composerMode}
                   replyTo={pendingDraft?.replyTo ?? (selectedEmail ? {
                     from: selectedEmail.from,
+                    replyToAddresses: selectedEmail.replyTo,
                     to: selectedEmail.to,
                     cc: selectedEmail.cc,
                     bcc: selectedEmail.bcc,
diff --git a/components/email/email-composer.tsx b/components/email/email-composer.tsx
index a32d2845..fe07bc4a 100644
--- a/components/email/email-composer.tsx
+++ b/components/email/email-composer.tsx
@@ -77,6 +77,7 @@ interface EmailComposerProps {
   mode?: 'compose' | 'reply' | 'replyAll' | 'forward';
   replyTo?: {
     from?: { email?: string; name?: string }[];
+    replyToAddresses?: { email?: string; name?: string }[];
     to?: { email?: string; name?: string }[];
     cc?: { email?: string; name?: string }[];
     bcc?: { email?: string; name?: string }[];
@@ -107,13 +108,15 @@ export function EmailComposer({
   // Initialize with reply/forward data if provided
   const getInitialTo = () => {
     if (!replyTo) return "";
+    // RFC 5322: use Reply-To header if present, otherwise fall back to From
+    const replyTarget = replyTo.replyToAddresses?.length
+      ? replyTo.replyToAddresses.filter(r => r.email).map(r => r.email).join(", ")
+      : replyTo.from?.[0]?.email || "";
     if (mode === 'reply') {
-      const email = replyTo.from?.[0]?.email || "";
-      return email ? email + ', ' : "";
+      return replyTarget ? replyTarget + ', ' : "";
     } else if (mode === 'replyAll') {
-      const from = replyTo.from?.[0]?.email || "";
       const originalTo = replyTo.to?.filter(r => r.email).map(r => r.email).join(", ") || "";
-      const combined = [from, originalTo].filter(Boolean).join(", ");
+      const combined = [replyTarget, originalTo].filter(Boolean).join(", ");
       return combined ? combined + ', ' : "";
     }
     return "";
diff --git a/lib/jmap/client.ts b/lib/jmap/client.ts
index 154d4125..b3ecc7e3 100644
--- a/lib/jmap/client.ts
+++ b/lib/jmap/client.ts
@@ -1648,19 +1648,28 @@ export class JMAPClient implements IJMAPClient {
     }
 
     let finalIdentityId = identityId;
-    if (!finalIdentityId) {
+    let identityReplyTo: EmailAddress[] | undefined;
+    {
       const identityResponse = await this.request([
         ["Identity/get", { accountId: this.accountId }, "0"]
       ]);
 
-      finalIdentityId = this.accountId;
+      if (!finalIdentityId) {
+        finalIdentityId = this.accountId;
+      }
       if (identityResponse.methodResponses?.[0]?.[0] === "Identity/get") {
-        const identities = (identityResponse.methodResponses[0][1].list || []) as { id: string; email: string }[];
+        const identities = (identityResponse.methodResponses[0][1].list || []) as Identity[];
         if (identities.length > 0) {
-          const target = fromEmail || this.username;
-          const matchingIdentity = identities.find((id) => id.email === target)
-            || (!target.includes('@') ? identities.find((id) => id.email.split('@')[0] === target) : undefined);
-          finalIdentityId = matchingIdentity?.id || identities[0].id;
+          if (!identityId) {
+            const target = fromEmail || this.username;
+            const matchingIdentity = identities.find((id) => id.email === target)
+              || (!target.includes('@') ? identities.find((id) => id.email.split('@')[0] === target) : undefined);
+            finalIdentityId = matchingIdentity?.id || identities[0].id;
+            identityReplyTo = matchingIdentity?.replyTo || identities[0].replyTo;
+          } else {
+            const matchedIdentity = identities.find((id) => id.id === identityId);
+            identityReplyTo = matchedIdentity?.replyTo;
+          }
         }
       }
     }
@@ -1668,6 +1677,7 @@ export class JMAPClient implements IJMAPClient {
     // Always create a new email with the final body content
     const emailCreate: Record<string, unknown> = {
       from: [{ ...(fromName ? { name: fromName } : {}), email: fromEmail || this.username }],
+      replyTo: identityReplyTo?.length ? identityReplyTo : undefined,
       to: to.map(email => ({ email })),
       cc: cc?.map(email => ({ email })),
       bcc: bcc?.map(email => ({ email })),