Add configurable rate limit option

src/client/index.ts

@@ -37,6 +37,7 @@ export const vOnEmailEventArgs = v.object({
 
 type Config = RuntimeConfig & {
   webhookSecret: string;
+  rateLimitMs: number;
 };
 
 function getDefaultConfig(): Config {
@@ -46,6 +47,7 @@ function getDefaultConfig(): Config {
     initialBackoffMs: 30000,
     retryAttempts: 5,
     testMode: true,
+    rateLimitMs: 600,
   };
 }
 
@@ -82,6 +84,13 @@ export type ResendOptions = {
    */
   testMode?: boolean;
 
+  /**
+   * The minimum time in milliseconds between API calls to Resend.
+   * Default is 600ms. Only change this if you have a higher rate limit
+   * approved by Resend.
+   */
+  rateLimitMs?: number;
+
   /**
    * A mutation to run after an email event occurs.
    * The mutation will be passed the email id and the event.
@@ -112,6 +121,7 @@ async function configToRuntimeConfig(
     initialBackoffMs: config.initialBackoffMs,
     retryAttempts: config.retryAttempts,
     testMode: config.testMode,
+    rateLimitMs: config.rateLimitMs,
     onEmailEvent: onEmailEvent
       ? { fnHandle: await createFunctionHandle(onEmailEvent) }
       : undefined,
@@ -225,6 +235,7 @@ export class Resend {
         options?.initialBackoffMs ?? defaultConfig.initialBackoffMs,
       retryAttempts: options?.retryAttempts ?? defaultConfig.retryAttempts,
       testMode: options?.testMode ?? defaultConfig.testMode,
+      rateLimitMs: options?.rateLimitMs ?? defaultConfig.rateLimitMs,
     };
     if (options?.onEmailEvent) {
       this.onEmailEvent = options.onEmailEvent;

src/component/lib.test.ts

@@ -264,6 +264,7 @@ describe("sendEmail with templates", () => {
         initialBackoffMs: 1000,
         retryAttempts: 3,
         testMode: true,
+        rateLimitMs: 600,
       },
       from: "test@resend.dev",
       to: ["delivered@resend.dev"],
@@ -301,6 +302,7 @@ describe("sendEmail with templates", () => {
           initialBackoffMs: 1000,
           retryAttempts: 3,
           testMode: true,
+          rateLimitMs: 600,
         },
         from: "test@resend.dev",
         to: ["delivered@resend.dev"],
@@ -323,6 +325,7 @@ describe("sendEmail with templates", () => {
         initialBackoffMs: 1000,
         retryAttempts: 3,
         testMode: true,
+        rateLimitMs: 600,
       },
       from: "test@resend.dev",
       to: ["delivered@resend.dev"],
@@ -357,6 +360,7 @@ describe("sendEmail with templates", () => {
           initialBackoffMs: 1000,
           retryAttempts: 3,
           testMode: true,
+          rateLimitMs: 600,
         },
         from: "test@resend.dev",
         to: ["delivered@resend.dev"],
@@ -372,6 +376,7 @@ describe("sendEmail with templates", () => {
           initialBackoffMs: 1000,
           retryAttempts: 3,
           testMode: true,
+          rateLimitMs: 600,
         },
         from: "test@resend.dev",
         to: ["delivered@resend.dev"],

src/component/lib.ts

@@ -21,7 +21,7 @@ import {
   vTemplate,
 } from "./shared.js";
 import type { FunctionHandle } from "convex/server";
-import type { EmailEvent, RunMutationCtx, RunQueryCtx } from "./shared.js";
+import type { EmailEvent } from "./shared.js";
 import { isDeepEqual } from "remeda";
 import schema from "./schema.js";
 import { omit } from "convex-helpers";
@@ -81,7 +81,7 @@ const callbackPool = new Workpool(components.callbackWorkpool, {
 });
 
 // We rate limit our calls to the Resend API.
-// FUTURE -- make this rate configurable if an account ups its sending rate with Resend.
+// This is used for the default rate limit (600ms). Custom rates use timestamp-based limiting.
 const resendApiRateLimiter = new RateLimiter(components.rateLimiter, {
   resendApi: {
     kind: "fixed window",
@@ -443,7 +443,8 @@ export const makeBatch = internalMutation({
     }
 
     // Okay, let's calculate rate limiting as best we can globally in this distributed system.
-    const delay = await getDelay(ctx);
+    const rateLimitMs = options.rateLimitMs ?? RESEND_ONE_CALL_EVERY_MS;
+    const delay = await getDelay(ctx, rateLimitMs);
 
     // Give the batch to the workpool! It will call the Resend batch API
     // in a durable background action.
@@ -707,13 +708,36 @@ async function createResendBatchPayload(
 }
 
 const FIXED_WINDOW_DELAY = 100;
-async function getDelay(ctx: RunMutationCtx & RunQueryCtx): Promise<number> {
-  const limit = await resendApiRateLimiter.limit(ctx, "resendApi", {
-    reserve: true,
-  });
-  //console.log(`RL: ${limit.ok} ${limit.retryAfter}`);
+async function getDelay(
+  ctx: MutationCtx,
+  rateLimitMs: number,
+): Promise<number> {
   const jitter = Math.random() * FIXED_WINDOW_DELAY;
-  return limit.retryAfter ? limit.retryAfter + jitter : 0;
+
+  // Use default rate limiter for standard rate (most users)
+  if (rateLimitMs === RESEND_ONE_CALL_EVERY_MS) {
+    const limit = await resendApiRateLimiter.limit(ctx, "resendApi", {
+      reserve: true,
+    });
+    return limit.retryAfter ? limit.retryAfter + jitter : 0;
+  }
+
+  // For custom rates, use timestamp-based approach
+  const lastOptions = await ctx.db.query("lastOptions").unique();
+  const now = Date.now();
+  const lastCallTime = lastOptions?.lastApiCallTime ?? 0;
+  const elapsed = now - lastCallTime;
+  const delay = Math.max(0, rateLimitMs - elapsed);
+  const totalDelay = delay + jitter;
+
+  // Reserve the slot by updating timestamp (include jitter to avoid under-reservation)
+  if (lastOptions) {
+    await ctx.db.patch(lastOptions._id, {
+      lastApiCallTime: now + totalDelay,
+    });
+  }
+
+  return totalDelay;
 }
 
 // Helper to fetch content by id. We'll use batch apis here to avoid lots of action->query calls.

src/component/schema.ts

@@ -14,6 +14,7 @@ export default defineSchema({
   }),
   lastOptions: defineTable({
     options: vOptions,
+    lastApiCallTime: v.optional(v.number()),
   }),
   deliveryEvents: defineTable({
     emailId: v.id("emails"),

src/component/setup.test.ts

@@ -155,6 +155,7 @@ export const createTestRuntimeConfig = (): RuntimeConfig => ({
   testMode: true,
   initialBackoffMs: 1000,
   retryAttempts: 3,
+  rateLimitMs: 600,
 });
 
 export const setupTestLastOptions = (

src/component/shared.ts

@@ -38,6 +38,7 @@ export const vOptions = v.object({
   apiKey: v.string(),
   testMode: v.boolean(),
   onEmailEvent: v.optional(onEmailEvent),
+  rateLimitMs: v.number(),
 });
 
 export type RuntimeConfig = Infer<typeof vOptions>;