通过Gmail API发送包含纯文本后备的HTML电子邮件

StackOverflow上一个已回答的问题表明,在电子邮件正文中添加html-markup就可以了.这个解决方案是否正确

但是,如果收件人的电子邮件服务器/客户端不支持HTML电子邮件呢？

例如,当使用Apache commons电子邮件时,我会执行以下操作:

// set the html message
email.setHtmlMsg("Our logo - ");
// set the alternative message
email.setTextMsg("Your email client does not support HTML messages");

如果收件人电子邮件服务器/客户端不支持HTML,有没有办法告诉Gmail API哪些电子邮件会退回？

PS我对Java代码示例特别感兴趣.

谢谢

要给出两个替代方案,您可以设置Content-Typeto mixed/alternative而不是:text/plain或者text/html:

如果我们想在尝试了这一点API探险家,我们只是使用Base64编码的邮件,并使其网址安全的所有替换/与_和所有+与-.

在开发者控制台中:

btoa(
  "Subject: Example Subject\r\n" +
  "From: \r\n" +
  "To: \r\n" +
  "Content-Type: multipart/alternative; boundary=\"foo_bar\"\r\n\r\n" +

  "--foo_bar\r\n" +
  "Content-Type: text/plain; charset=UTF-8\r\n\r\n" +

  "*Bold example message text*\r\n\r\n" +

  "--foo_bar\r\n" +
  "Content-Type: text/html; charset=UTF-8\r\n\r\n" +

  "
Bold example message text
\r\n\r\n" +

  "--foo_bar--" 
).replace(/\+/g, '-').replace(/\//g, '_');

POST https://www.googleapis.com/gmail/v1/users/me/messages/send?access_token={YOUR_API_KEY}

{
 "raw": "U3ViamVjdDogRXhhbXBsZSBTdWJqZWN0DQpGcm9tOiA8ZXhhbXBsZUBnbWFpbC5jb20-DQpUbzogPGV4YW1wbGVAZ21haWwuY29tPg0KQ29udGVudC1UeXBlOiBtdWx0aXBhcnQvYWx0ZXJuYXRpdmU7IGJvdW5kYXJ5PSJmb29fYmFyIg0KDQotLWZvb19iYXINCkNvbnRlbnQtVHlwZTogdGV4dC9wbGFpbjsgY2hhcnNldD1VVEYtOA0KDQoqQm9sZCBleGFtcGxlIG1lc3NhZ2UgdGV4dCoNCg0KLS1mb29fYmFyDQpDb250ZW50LVR5cGU6IHRleHQvaHRtbDsgY2hhcnNldD1VVEYtOA0KDQo8ZGl2IGRpcj0ibHRyIj48Yj5Cb2xkIGV4YW1wbGUgbWVzc2FnZSB0ZXh0PC9iPjwvZGl2Pg0KDQotLWZvb19iYXItLQ=="
}

要在Java中执行等效操作,您可以:

Message message = new MimeMessage(session);
Multipart multiPart = new MimeMultipart("alternative");

MimeBodyPart textPart = new MimeBodyPart();
textPart.setText(text, "utf-8");

MimeBodyPart htmlPart = new MimeBodyPart();
htmlPart.setContent(html, "text/html; charset=utf-8");

multiPart.addBodyPart(textPart); 
multiPart.addBodyPart(htmlPart);
message.setContent(multiPart);

ByteArrayOutputStream output = new ByteArrayOutputStream();
message.writeTo(output);
String rawEmail = Base64.encodeBase64URLSafeString(output.toByteArray());

Message message = new Message();
message.setRaw(rawEmail);
message = service.users().messages().send(userId, message).execute();