From nediv.arrl.org:
Earlier today, ARRL life members received an email from the Membership Department asking them to verify that their membership ID and address information were correct. Many people were rightfully suspicious, thinking the message was a possible phishing attempt.
ARRL CEO David Minster, NA2AA, confirmed late this afternoon that the message was, in fact, legitimate and there was no need for concern. ARRL asks that you reply to the email with the appropriate response.