Php - 发送带有多个加密附件的加密邮件，可读取Outlook

Question

任何人都可以解释如何加密具有多个附件的mime邮件，可读取Outlook吗？我目前构建一个多部分邮件，由Outlook正确读取，但如果我使用openssl_pkcs7_encrypt（）加密那个multipart-headers +正文，Outlook只会读取（html）-body并且无法分离附件。然后它将第一个附件说成不可读。

结构是

    To: you@example.com
    From: me@example.com
    Reply-To: me@example.com
    MIME-Version: 1.0
    Content-Type: multipart/mixed; boundary="mx-2041315b16859f651fe7575c5949d1aa"
    This is a multi-part message in MIME format

    --mx-2041315b16859f651fe7575c5949d1aa
    Content-Type: multipart/related; boundary="rel-2041315b16859f651fe7575c5949d1aa";

    --rel-2041315b16859f651fe7575c5949d1aa
    Content-Type: text/html; charset=UTF-8;

    [html-content here...]

    --rel-2041315b16859f651fe7575c5949d1aa
    Content-Type: image/jpg; name="Image.jpg"
    Content-ID: img1
    Content-Disposition: inline; filename="Image.jpg"
    Content-Transfer-Encoding: base64

    [related base64-encoded JPEG...]

    --rel-2041315b16859f651fe7575c5949d1aa
    --mx-2041315b16859f651fe7575c5949d1aa
    Content-Type: application/octet-stream; name="A_PDF.pdf"
    Content-Transfer-Encoding: base64
    Content-Disposition: attachment; filename="A_PDF.pdf"

    [base64-encoded PDF...]

    --mx-2041315b16859f651fe7575c5949d1aa