diff --git a/src/app/mail/index.ts b/src/app/mail/index.ts
index 64127ff3..1e504659 100644
--- a/src/app/mail/index.ts
+++ b/src/app/mail/index.ts
@@ -1,4 +1,4 @@
-import {hash, maybe, spec, throttle} from "@welshman/lib"
+import {call, hash, maybe, spec, throttle} from "@welshman/lib"
 import type {Filter} from "@welshman/util"
 import {Address, DELETE, MESSAGE, makeEvent, makeHttpAuth, makeHttpAuthHeader} from "@welshman/util"
 import {merged} from "@welshman/store"
@@ -75,50 +75,70 @@ const syncRelaySubscriptionsForEmail = (
 export class MailNotifications {
   _controller = maybe<AbortController>()
 
+  // In-flight register promise, so overlapping calls (settings page submit plus
+  // Mail.sync) coalesce into a single PUT instead of racing two subscriptions.
+  _register = maybe<Promise<void>>()
+
   async register(email: string, frequency: string) {
-    const $user = User.require(app.get())
-    const $signer = $user.signer
+    if (this._register) return this._register
 
-    if (!$signer) {
-      emailNotificationState.set({error: "No signer available. Check your browser extension."})
-      throw new Error("No signer available")
-    }
+    this._register = call(async () => {
+      try {
+        const $user = User.require(app.get())
+        const $signer = $user.signer
 
-    if (!EMAIL_NOTIFICATION_SERVER) {
-      emailNotificationState.set({error: "Email notification server is not configured."})
-      throw new Error("Email notification server not configured")
-    }
+        if (!$signer) {
+          emailNotificationState.set({
+            error: "No signer available. Check your browser extension.",
+          })
+          throw new Error("No signer available")
+        }
 
-    let authEvent
-    try {
-      authEvent = await $signer.sign(await makeHttpAuth(EMAIL_NOTIFICATION_SERVER, "PUT"))
-    } catch (e) {
-      emailNotificationState.set({error: "Failed to create authentication. Check your signer."})
-      throw new Error("Failed to sign NIP-98 auth", {cause: e})
-    }
+        if (!EMAIL_NOTIFICATION_SERVER) {
+          emailNotificationState.set({error: "Email notification server is not configured."})
+          throw new Error("Email notification server not configured")
+        }
 
-    const authHeader = makeHttpAuthHeader(authEvent)
+        let authEvent
+        try {
+          authEvent = await $signer.sign(await makeHttpAuth(EMAIL_NOTIFICATION_SERVER, "PUT"))
+        } catch (e) {
+          emailNotificationState.set({
+            error: "Failed to create authentication. Check your signer.",
+          })
+          throw new Error("Failed to sign NIP-98 auth", {cause: e})
+        }
 
-    let res
-    try {
-      res = await fetch(buildUrl(EMAIL_NOTIFICATION_SERVER, "subscription", "email"), {
-        method: "PUT",
-        body: JSON.stringify({email, frequency, pubkey: $user.pubkey}),
-        headers: {Authorization: authHeader, "Content-Type": "application/json"},
-      })
-    } catch (e) {
-      emailNotificationState.set({error: `Could not reach email server. Check your connection.`})
-      throw new Error("Network error", {cause: e})
-    }
+        const authHeader = makeHttpAuthHeader(authEvent)
 
-    if (!res.ok) {
-      const text = await res.text().catch(() => "unknown error")
-      emailNotificationState.set({error: `Registration failed: ${text}`})
-      throw new Error(`Registration failed: ${text}`)
-    }
+        let res
+        try {
+          res = await fetch(buildUrl(EMAIL_NOTIFICATION_SERVER, "subscription", "email"), {
+            method: "PUT",
+            body: JSON.stringify({email, frequency, pubkey: $user.pubkey}),
+            headers: {Authorization: authHeader, "Content-Type": "application/json"},
+          })
+        } catch (e) {
+          emailNotificationState.set({
+            error: `Could not reach email server. Check your connection.`,
+          })
+          throw new Error("Network error", {cause: e})
+        }
 
-    const {key, callback} = await res.json()
-    emailNotificationState.set({key, callback, email, frequency, error: undefined})
+        if (!res.ok) {
+          const text = await res.text().catch(() => "unknown error")
+          emailNotificationState.set({error: `Registration failed: ${text}`})
+          throw new Error(`Registration failed: ${text}`)
+        }
+
+        const {key, callback} = await res.json()
+        emailNotificationState.set({key, callback, email, frequency, error: undefined})
+      } finally {
+        this._register = undefined
+      }
+    })
+
+    return this._register
   }
 
   async unregister() {