There is a library for Sending Email in Background which is working efficient.
You can get the library from here Background Mail Library
Now import this library in your eclipse, and then go to project properties and add this library to your project.
After all this process, just put these code in your project, and it will send email in background.
BackgroundMail bm = new BackgroundMail(context);
bm.setGmailUserName("sendername@gmail.com");
bm.setGmailPassword("sender_email_password");
bm.setMailTo("receiver@gmail.com");
bm.setFormSubject("Subject");
bm.setFormBody("Body");
bm.send();
With this permissions
Update 1: Updated the Library name
