diff --git a/apps/api/src/modules/mail/__tests__/mail-service-send.test.ts b/apps/api/src/modules/mail/__tests__/mail-service-send.test.ts
new file mode 100644
index 0000000..8ff25d5
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+++ b/apps/api/src/modules/mail/__tests__/mail-service-send.test.ts
@@ -0,0 +1,108 @@
+/** 发信:先落 sending 再发;厂商失败落 failed 不抛;幂等键不发两封、失败可重发;附件取自 upload;from 对账号 */
+import { describe, expect, it } from 'vitest';
+import { MailAccountNotFoundError, MailNoDefaultAccountError, MailSecretMissingError, MailSendInvalidError } from '../contract.ts';
+import { createMailService } from '../internal/usecase/mail-service.ts';
+import { createPostalMimeParser } from '../internal/adapter/postal-mime-parser.ts';
+import { account, fakeProvider, fixedClock, memoryAccounts, memoryAttachments, memoryInbound, memoryOutbound, plainSecrets, seqIds } from './fakes.ts';
+
+function harness() {
+  const clock = fixedClock();
+  const accounts = memoryAccounts(clock);
+  const outbound = memoryOutbound();
+  const attachments = memoryAttachments();
+  const imap = fakeProvider('imap-smtp');
+  const wecom = fakeProvider('wecom');
+  const service = createMailService({
+    accounts,
+    inbound: memoryInbound(),
+    outbound,
+    attachments,
+    providers: { 'imap-smtp': imap, wecom },
+    mime: createPostalMimeParser(),
+    secrets: plainSecrets,
+    clock,
+    ids: seqIds('out'),
+    notify: { changed: () => undefined },
+  });
+  return { service, accounts, outbound, attachments, imap, clock };
+}
+const base = { to: ['b@acme.com'], cc: [], bcc: [], subject: '报价', text: '见附件', references: [], attachments: [], requestedBy: { kind: 'ops' as const } };
+
+describe('send', () => {
+  it('默认账号发出:留痕 sent、Message-ID 是 <id@域>、发件人带显示名、返回 providerRef', async () => {
+    const h = harness();
+    await h.accounts.save(account());
+    const result = await h.service.send(base);
+    expect(result).toEqual({ outboundId: 'out-1', accountId: 'acc-1', messageId: '<out-1@we.com>', state: 'sent', providerRef: 'fake:1' });
+    expect(h.imap.sent[0]?.from).toEqual({ address: 'sales@we.com', name: '销售部' });
+    expect(h.imap.sent[0]?.messageId).toBe('<out-1@we.com>');
+    const row = h.outbound.rows.get('out-1');
+    expect(row?.state).toBe('sent');
+    expect(row?.sentAt).toEqual(h.clock.now());
+    expect((await h.service.listOutbound({}))[0]).toMatchObject({ id: 'out-1', state: 'sent', to: ['b@acme.com'] });
+  });
+
+  it('厂商失败:落 failed(原话脱敏)、不抛、返回 state=failed', async () => {
+    const h = harness();
+    await h.accounts.save(account());
+    h.imap.failSendWith(Object.assign(new Error('Invalid login'), { response: '535 5.7.8 pw-1234 rejected' }));
+    const result = await h.service.send(base);
+    expect(result.state).toBe('failed');
+    expect(result.error).toBe('Invalid login —— 535 5.7.8 *** rejected');
+    expect(h.outbound.rows.get('out-1')?.state).toBe('failed');
+  });
+
+  it('幂等键:已 sent 的直接回原结果不再发;失败的那一行复用重发', async () => {
+    const h = harness();
+    await h.accounts.save(account());
+    h.imap.failSendWith(new Error('暂时不行'));
+    const failed = await h.service.send({ ...base, idempotencyKey: 'k-1' });
+    expect(failed.state).toBe('failed');
+    h.imap.failSendWith(undefined);
+    const retried = await h.service.send({ ...base, idempotencyKey: 'k-1' });
+    expect(retried).toMatchObject({ outboundId: failed.outboundId, state: 'sent' });
+    const again = await h.service.send({ ...base, idempotencyKey: 'k-1' });
+    expect(again).toMatchObject({ outboundId: failed.outboundId, state: 'sent' });
+    expect(h.imap.sent).toHaveLength(1);
+    expect(h.outbound.rows.size).toBe(1);
+  });
+
+  it('入参问题抛而不落行:无正文 400、没默认账号 412、from 对不上 404、凭证空 412', async () => {
+    const h = harness();
+    await expect(h.service.send(base)).rejects.toBeInstanceOf(MailNoDefaultAccountError);
+    await h.accounts.save(account());
+    await expect(h.service.send({ ...base, text: undefined })).rejects.toBeInstanceOf(MailSendInvalidError);
+    await expect(h.service.send({ ...base, from: 'nobody@we.com' })).rejects.toBeInstanceOf(MailAccountNotFoundError);
+    await h.accounts.save(account({ secretCipher: null }));
+    await expect(h.service.send(base)).rejects.toBeInstanceOf(MailSecretMissingError);
+    expect(h.outbound.rows.size).toBe(0);
+  });
+
+  it('附件:uploadRef 取 upload 的字节与类型;dataBase64 直接用;两者都没有 400', async () => {
+    const h = harness();
+    await h.accounts.save(account());
+    const { ref } = await h.attachments.put({ name: 'q.pdf', contentType: 'application/pdf', bytes: new Uint8Array([1, 2]), note: '' });
+    await h.service.send({
+      ...base,
+      attachments: [
+        { name: 'q.pdf', contentType: 'application/octet-stream', uploadRef: ref },
+        { name: 'n.txt', contentType: 'text/plain', dataBase64: Buffer.from('hi').toString('base64') },
+      ],
+    });
+    expect(h.imap.sent[0]?.attachments.map((a) => [a.name, a.contentType, a.bytes.byteLength])).toEqual([
+      ['q.pdf', 'application/pdf', 2],
+      ['n.txt', 'text/plain', 2],
+    ]);
+    await expect(h.service.send({ ...base, attachments: [{ name: 'x', contentType: 'text/plain' }] })).rejects.toBeInstanceOf(MailSendInvalidError);
+    await expect(h.service.send({ ...base, attachments: [{ name: 'x', contentType: 'text/plain', uploadRef: 'up-404' }] })).rejects.toBeInstanceOf(MailSendInvalidError);
+  });
+
+  it('from 指定发件地址(channel 用):按地址找账号,inReplyTo / references 原样交给 provider', async () => {
+    const h = harness();
+    await h.accounts.save(account({ isDefault: false }));
+    const result = await h.service.send({ ...base, from: 'SALES@we.com', inReplyTo: '<m1@acme.com>', references: ['<m1@acme.com>'], requestedBy: { kind: 'channel', taskId: 't-1' } });
+    expect(result.accountId).toBe('acc-1');
+    expect(h.imap.sent[0]?.inReplyTo).toBe('<m1@acme.com>');
+    expect(h.outbound.rows.get('out-1')?.requestedBy).toEqual({ kind: 'channel', taskId: 't-1' });
+  });
+});