/**
  * Attach a file referenced by the given link.
  *
  * <p>
  * If you want to reference the attachment as inline image, provide content
  * id wrapped by angle brackets and refer the image with content id without
  * angle brackets.
  * </p>
  *
  * For example:
  *
  * <pre>
  * builder
  * 	.html("<img src='cid:logo.png'>")
  * 	.attach("logo.png", "/path/to/logo.png", "<logo.png>"
  * 	.send();
  * <pre>
  *
  * @param name
  *            attachment file name
  * @param link
  *            attachment file link (url or file path)
  * @param cid
  *            content id
  * @return this
  */
 public MailBuilder attach(String name, String link, String cid) {
   Preconditions.checkNotNull(link, "link can't be null");
   Content content = new Content();
   content.name = name;
   content.file = link;
   content.cid = cid;
   contents.add(content);
   textOnly = false;
   return this;
 }
 /**
  * Attach a file as inline content.
  *
  * @param name attachment file name
  * @param link attachment file link (url or file path)
  * @param inline whether to inline this attachment
  * @return this
  */
 public MailBuilder inline(String name, String link) {
   Preconditions.checkNotNull(link, "link can't be null");
   Content content = new Content();
   content.name = name;
   content.file = link;
   content.cid = "<" + name + ">";
   content.inline = true;
   contents.add(content);
   textOnly = false;
   return this;
 }