@AssertFalse(message = "'properties' and 'propertiesFile' are mutually exclusive")
	private boolean isInvalid() {
		return Exclusives.strictlyMoreThanOne(properties != null, propertiesFile != null);
	}
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