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If you have separated from SU (resigned your job, graduated, etc.) and no longer need your NetID, you don't need to do anything.
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When exactly do passwords expire?
Password expiration occurs once every day, even on Sundays, holidays, and while you're on vacation. When you are notified that it's time to change your password, please do so promptly. Expiration is scheduled to occur at 8:30am on the expiration date. The email notifications indicate "midnight", but it would be bad practice to disrupt access at a time when the ITS Service Center is closed.