VC++ 呼叫預設郵件用戶端發送 Email：ShellExecute 與 MAPI 兩種實作方式

一、簡單需求：僅啟動郵件用戶端

使用 ShellExecute 直接呼叫 mailto: 協定：

ShellExecute(NULL, NULL, "mailto:email@163.net", NULL, NULL, SW_SHOW);

適用於無需附件、主題、多收件人等進階需求的場景。

二、進階需求：支援附件、主題、多收件人 — MAPI 實作

動態載入 MAPI32.DLL，取得 MAPISendMail 函式指標，填寫 MapiMessage、MapiRecipDesc、MapiFileDesc 結構體發送郵件。

2.1 關鍵程式碼完整範例

#include "mapi.h"

void CSendEMailDlg::OnSendMapi() {
    UpdateData(true);

    // 1. 載入 MAPI32.DLL
    HMODULE hMod = LoadLibrary("MAPI32.DLL");
    if (!hMod) { AfxMessageBox(AFX_IDP_FAILED_MAPI_LOAD); return; }

    // 2. 取得 MAPISendMail 位址
    ULONG (PASCAL *lpfnSendMail)(ULONG, ULONG, MapiMessage*, FLAGS, ULONG);
    (FARPROC&)lpfnSendMail = GetProcAddress(hMod, "MAPISendMail");
    if (!lpfnSendMail) { AfxMessageBox(AFX_IDP_INVALID_MAPI_DLL); FreeLibrary(hMod); return; }

    // 3. 準備附件資訊 (動態陣列)
    int nFileCount = m_list.GetCount();
    MapiFileDesc* pFileDesc = (MapiFileDesc*)malloc(sizeof(MapiFileDesc) * nFileCount);
    memset(pFileDesc, 0, sizeof(MapiFileDesc) * nFileCount);
    TCHAR* pTchPath = (TCHAR*)malloc(MAX_PATH * nFileCount);

    CString szText;
    for (int i = 0; i < nFileCount; i++) {
        TCHAR* p = pTchPath + MAX_PATH * i;
        m_list.GetText(i, szText);
        _tcscpy(p, szText);
        (pFileDesc + i)->nPosition = (ULONG)-1;
        (pFileDesc + i)->lpszPathName = p;
        (pFileDesc + i)->lpszFileName = p;
    }

    // 4. 收件人資訊
    MapiRecipDesc recip = {0};
    recip.lpszAddress = m_szEmailMAPI.GetBuffer(0);
    recip.ulRecipClass = MAPI_TO;

    // 5. 郵件主體
    MapiMessage message = {0};
    message.nFileCount = nFileCount;
    message.lpFiles = pFileDesc;
    message.nRecipCount = 1;
    message.lpRecips = &recip;
    message.lpszSubject = m_szSubject.GetBuffer(0);
    message.lpszNoteText = m_szText.GetBuffer(0);

    // 6. 保存父視窗指標，發送後回復焦點
    CWnd* pParentWnd = CWnd::GetSafeOwner(NULL, NULL);

    // 7. 發送郵件 (顯示對話框讓使用者確認)
    int nError = lpfnSendMail(0, 0, &message, MAPI_LOGON_UI | MAPI_DIALOG, 0);
    if (nError != SUCCESS_SUCCESS && nError != MAPI_USER_ABORT && nError != MAPI_E_LOGIN_FAILURE)
        AfxMessageBox(AFX_IDP_FAILED_MAPI_SEND);

    pParentWnd->SetActiveWindow();

    // 8. 釋放資源
    free(pFileDesc);
    free(pTchPath);
    FreeLibrary(hMod);
}

2.2 常見錯誤碼對照

三、總結

• ShellExecute：極簡、無依賴、功能受限。
• MAPI：功能完整、需動態載入 DLL、相容性佳（Outlook、Windows Mail、Foxmail 等均支援）。