Q:

How to send a batch with emails in android?

I want to send several emails to different recipients, but the text of the letters may differ. And I also want to authorize the user and send mail on his behalf, by Intent and the built-in mail client app. And is there any way to do this with one button click, rather than calling up a new email window (activity) for each of these letters and forcing the user to confirms the sending of each letter?
And is there any way to not call the new e-mail window for each of these letters, so that the user confirms the sending of each letter, and do this at the touch of a button?
Maybe are there any third-party libraries or free mail services for this purpose?

A:

You can use simple-java-mail to achieve that. 
public static void SendMail(String recipientName,String recipientAddress,String subject,String message,File file,String myAdress,String password) throws IOException{

            System.out.println("File size "+file.length());

 Email email = new Email();
 email.setFromAddress(myAdress.split("@")[0], myAdress);
 email.addRecipient(recipientName, recipientAddress, Message.RecipientType.TO);
 email.setSubject(subject);
 email.setText(message);
 if(file!=null)
 email.addAttachment(file.getName(), 
FileUtils.readFileToByteArray(file),"application/pdf");

 String host = myAdress.split("@")[1];
  new Mailer(
    new ServerConfig("smtp."+host, 587, myAdress, password),
    TransportStrategy.SMTP_TLS,
    new ProxyConfig("socksproxy."+host, 1080, "proxy user", "proxy password")
 ).sendMail(email);

}

If your client is using Gmail, they have to allow third parties to send mail in their settings

