Reset Office 365 password expiration policy

This guidance applies to Office 365 Enterprise, Office 365 Business Essentials or Office 365 Business Premium.

User passwords expire on a regular basis in Office 365. This setting is a default established by Microsoft when tenancies are established. If you are a Global Admins you can change the number of days before users are notified of password expiration. Password expiration policies can also be set so that passwords never expire.

1. Sign in to Office 365 with your account
2. Go to the Office 365 admin center
3. Go to <Support > PSecurity & Privacy>
4. Find Password policy section and click <Edit>
5. If you want user passwords to expire, type the number of days before the password should expire. Choose a number of days from 14 to 730.
6. Type the number of days before users are notified that their password will expire, and then click <Save>. Choose a number of days from 1 to 30.

See Microsoft Office 365 Support page