jodd-mail/src/main/java/jodd/mail/ReceivedEmail.java
protected static String parseContentId(final Part part) throws MessagingException {
		if (part instanceof MimePart) {
			final MimePart mp = (MimePart) part;
			return mp.getContentID();
		} else {
			return null;
		}
	}
protected static String parseContentId(final Part part) throws MessagingException {
		if (part instanceof MimePart) {
			final MimePart mp = (MimePart) part;
			return mp.getContentID();
		} else {
			return null;
		}
	}
Returns the Content-ID of this {@link Part}. Returns {@code null} if none present.

@param part {@link Part} the Part to parse.
@return String containing content ID.
@throws MessagingException if there is a failure.
@see MimePart#getContentID()