+ Validate an email address using three techniques:
+
+ * Ensuring that the length of local and domain parts is within the
+ RFC-specified limits.
+ * A syntax check using a regular expression, or the full RFC 5322
+ grammar.
+ * Confirmation of valid @MX@ records (or, optionally, @A@
+ records) for the domain.
+
+ A complete description, options, and examples can be found in the
+ man page.