diff --git a/src/index.ts b/src/index.ts
index d3e97719..ab2f8c38 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -11,7 +11,7 @@ export * from './emails/attachments/interfaces';
 export * from './emails/interfaces';
 export * from './emails/receiving/interfaces';
 export type { ErrorResponse, Response } from './interfaces';
-export { Resend } from './resend';
+export { Resend, type ResendOptions } from './resend';
 export * from './segments/interfaces';
 export * from './templates/interfaces';
 export * from './topics/interfaces';
diff --git a/src/resend.spec.ts b/src/resend.spec.ts
new file mode 100644
index 00000000..7935b658
--- /dev/null
+++ b/src/resend.spec.ts
@@ -0,0 +1,135 @@
+import createFetchMock from 'vitest-fetch-mock';
+import { Resend } from './resend';
+import { mockSuccessResponse } from './test-utils/mock-fetch';
+
+const fetchMocker = createFetchMock(vi);
+fetchMocker.enableMocks();
+
+describe('Resend', () => {
+  afterEach(() => fetchMock.resetMocks());
+  afterAll(() => fetchMocker.disableMocks());
+
+  describe('constructor options', () => {
+    it('uses default baseUrl and userAgent when no options provided', () => {
+      const resend = new Resend('re_zKa4RCko_Lhm9ost2YjNCctnPjbLw8Nop');
+
+      expect(resend.baseUrl).toBe('https://api.resend.com');
+      expect(resend.userAgent).toMatch(/^resend-node:/);
+    });
+
+    it('uses custom baseUrl when options.baseUrl is provided', () => {
+      const customBaseUrl = 'https://eu.api.resend.com';
+      const resend = new Resend('re_zKa4RCko_Lhm9ost2YjNCctnPjbLw8Nop', {
+        baseUrl: customBaseUrl,
+      });
+
+      expect(resend.baseUrl).toBe(customBaseUrl);
+    });
+
+    it('uses custom userAgent when options.userAgent is provided', () => {
+      const customUserAgent = 'my-app/1.0';
+      const resend = new Resend('re_zKa4RCko_Lhm9ost2YjNCctnPjbLw8Nop', {
+        userAgent: customUserAgent,
+      });
+
+      expect(resend.userAgent).toBe(customUserAgent);
+    });
+
+    it('uses both custom baseUrl and userAgent when both provided', () => {
+      const resend = new Resend('re_zKa4RCko_Lhm9ost2YjNCctnPjbLw8Nop', {
+        baseUrl: 'https://custom.api.com',
+        userAgent: 'custom-agent/2.0',
+      });
+
+      expect(resend.baseUrl).toBe('https://custom.api.com');
+      expect(resend.userAgent).toBe('custom-agent/2.0');
+    });
+
+    it('uses RESEND_BASE_URL from env when no options.baseUrl provided', () => {
+      const originalEnv = process.env;
+      process.env = {
+        ...originalEnv,
+        RESEND_BASE_URL: 'https://env-base-url.example.com',
+      };
+
+      const resend = new Resend('re_zKa4RCko_Lhm9ost2YjNCctnPjbLw8Nop');
+      expect(resend.baseUrl).toBe('https://env-base-url.example.com');
+
+      process.env = originalEnv;
+    });
+
+    it('uses RESEND_USER_AGENT from env when no options.userAgent provided', () => {
+      const originalEnv = process.env;
+      process.env = {
+        ...originalEnv,
+        RESEND_USER_AGENT: 'env-user-agent/1.0',
+      };
+
+      const resend = new Resend('re_zKa4RCko_Lhm9ost2YjNCctnPjbLw8Nop');
+      expect(resend.userAgent).toBe('env-user-agent/1.0');
+
+      process.env = originalEnv;
+    });
+
+    it('options.baseUrl overrides RESEND_BASE_URL env', () => {
+      const originalEnv = process.env;
+      process.env = {
+        ...originalEnv,
+        RESEND_BASE_URL: 'https://env-base-url.example.com',
+      };
+
+      const resend = new Resend('re_zKa4RCko_Lhm9ost2YjNCctnPjbLw8Nop', {
+        baseUrl: 'https://options-base-url.example.com',
+      });
+      expect(resend.baseUrl).toBe('https://options-base-url.example.com');
+
+      process.env = originalEnv;
+    });
+
+    it('options.userAgent overrides RESEND_USER_AGENT env', () => {
+      const originalEnv = process.env;
+      process.env = {
+        ...originalEnv,
+        RESEND_USER_AGENT: 'env-user-agent/1.0',
+      };
+
+      const resend = new Resend('re_zKa4RCko_Lhm9ost2YjNCctnPjbLw8Nop', {
+        userAgent: 'options-user-agent/2.0',
+      });
+      expect(resend.userAgent).toBe('options-user-agent/2.0');
+
+      process.env = originalEnv;
+    });
+  });
+
+  describe('fetchRequest with custom options', () => {
+    it('sends request to custom baseUrl', async () => {
+      const customBaseUrl = 'https://custom.api.resend.com';
+      const resend = new Resend('re_zKa4RCko_Lhm9ost2YjNCctnPjbLw8Nop', {
+        baseUrl: customBaseUrl,
+      });
+
+      mockSuccessResponse({ id: 'key-123' }, { headers: {} });
+
+      await resend.apiKeys.list();
+
+      const [url] = fetchMock.mock.calls[0];
+      expect(url).toBe(`${customBaseUrl}/api-keys`);
+    });
+
+    it('sends custom User-Agent in request headers', async () => {
+      const customUserAgent = 'my-integration/3.0';
+      const resend = new Resend('re_zKa4RCko_Lhm9ost2YjNCctnPjbLw8Nop', {
+        userAgent: customUserAgent,
+      });
+
+      mockSuccessResponse({ id: 'key-123' }, { headers: {} });
+
+      await resend.apiKeys.list();
+
+      const requestOptions = fetchMock.mock.calls[0][1];
+      const headers = requestOptions?.headers as Headers;
+      expect(headers.get('User-Agent')).toBe(customUserAgent);
+    });
+  });
+});
diff --git a/src/resend.ts b/src/resend.ts
index a19f3754..e206da37 100644
--- a/src/resend.ts
+++ b/src/resend.ts
@@ -17,16 +17,27 @@ import { Webhooks } from './webhooks/webhooks';
 
 const defaultBaseUrl = 'https://api.resend.com';
 const defaultUserAgent = `resend-node:${version}`;
-const baseUrl =
-  typeof process !== 'undefined' && process.env
+
+function getDefaultBaseUrl(): string {
+  return typeof process !== 'undefined' && process.env
     ? process.env.RESEND_BASE_URL || defaultBaseUrl
     : defaultBaseUrl;
-const userAgent =
-  typeof process !== 'undefined' && process.env
+}
+
+function getDefaultUserAgent(): string {
+  return typeof process !== 'undefined' && process.env
     ? process.env.RESEND_USER_AGENT || defaultUserAgent
     : defaultUserAgent;
+}
+
+export interface ResendOptions {
+  baseUrl?: string;
+  userAgent?: string;
+}
 
 export class Resend {
+  readonly baseUrl: string;
+  readonly userAgent: string;
   private readonly headers: Headers;
 
   readonly apiKeys = new ApiKeys(this);
@@ -45,7 +56,10 @@ export class Resend {
   readonly templates = new Templates(this);
   readonly topics = new Topics(this);
 
-  constructor(readonly key?: string) {
+  constructor(
+    readonly key?: string,
+    options?: ResendOptions,
+  ) {
     if (!key) {
       if (typeof process !== 'undefined' && process.env) {
         this.key = process.env.RESEND_API_KEY;
@@ -58,16 +72,19 @@ export class Resend {
       }
     }
 
+    this.baseUrl = options?.baseUrl ?? getDefaultBaseUrl();
+    this.userAgent = options?.userAgent ?? getDefaultUserAgent();
+
     this.headers = new Headers({
       Authorization: `Bearer ${this.key}`,
-      'User-Agent': userAgent,
+      'User-Agent': this.userAgent,
       'Content-Type': 'application/json',
     });
   }
 
   async fetchRequest<T>(path: string, options = {}): Promise<Response<T>> {
     try {
-      const response = await fetch(`${baseUrl}${path}`, options);
+      const response = await fetch(`${this.baseUrl}${path}`, options);
 
       if (!response.ok) {
         try {