@AssertTrue(message = "usePolling=false is only supported with imap(s)")
	private boolean isUsePollingValid() {
		if (!usePolling) {
			return protocol == imap || protocol == imaps;
		}
		else {
			return true;
		}
	}
Captures options for the {@code mail} source module.

@author Eric Bottard
@author Gary Russell
@author Ilayaperumal Gopinathan
extensions/spring-xd-extension-mail/src/main/java/org/springframework/xd/mail/MailSourceOptionsMetadata.java